This PR adds XMPP transport to send secure messages only.

TODO/Features:

• [x] Add XMPP page into intro screen
• [x] Add new "XMPP address" message type to do not use a centralized directory
• [x] Add new XMPP message type when transport is set to XMPP
• [x] Switch to secure SMS if the recipient is offline
• [x] Allow user to use a custom XMPP server
• [x] Delete XMPP account if the user disables XMPP feature
• [x] Display a warning if the custom XMPP server doesn't support XEP-0198 Stream Management (required to do not lost messages when switching from a network to another or on unreliable connectivities)
• [x] Fix bad encryption with long XMPP messages
• [x] Display an XMPP icon for XMPP messages
• [x] Ask the user to optionally set up XMPP on first boot
• [x] Improve XMPP address sharing mechanism
• [x] Share XMPP address when a secure session is started
• [x] Implement a form to manually set up an XMPP address
• [ ] Fix recipient status (sometimes a recipient is seen as offline but it is actually online)
• [ ] Add support for XMPP media messages (for now, Silence crashes)
• [ ] Write documentation
• [ ] Include a list of trusted XMPP servers to allow users to register
• [ ] OMEMO?

This PR fixes #370 as a side effect because it starts Silence on boot. For now, the list of "trusted XMPP servers" only contains xmpp.silence.im, which is not designed to be used except for testing. We won't host an XMPP server in the short term.

CellTrust is currently trying to ban SMSSecure from app stores. The company claims that SMSSecure creates a confusion with their trademark SecureSMS.

We don't want to fight against fools and we will change the name of the app. This PR shows a notification to the user to focus on the new name.

Suggestions for the new name are opened and you can comment on this PR to make proposals. We have to find it very quickly as SMSSecure is not available on the Amazon App Store and on the US Play Store anymore.

The new name must not be a registered trademark (a directory of trademarks is available online) and its domain name should be available (at least .org and/or .im and/or .io).

I am always having problems redeeming my toppings with Vodafone. I already filed that Issue on https://github.com/WhisperSystems/TextSecure/issues/1780, but they were very reluctant to even cope with fixing it. I was wondering if you guys might be a little more open towards this Issue, which very likely does not just happen to be mine?

• Add files to secure conversations by selecting in app (after enabling the preference)
• Share files (up to mms-sizelimit) and attach them to a secure chat

We've been developing "panic button" features in our apps for years, and now we are working to make a more flexible and open ecosystem of apps that can both trigger other apps, or respond to triggers. Since SMSSecure already includes a "lock" feature, it is a natural panic responder app. This setup allows for easy configuration of a single trigger action which can then trigger multiple apps.

The first commit adds support for receiving the panic trigger. The second commit wipes SMSSecure from the Recent Apps when it is responding to a panic trigger.

More info on the panic kit work here: https://dev.guardianproject.info/projects/panic/wiki

The first panic button app that sends this kind of trigger is called Ripple, and it is available here: https://github.com/guardianproject/ripple https://play.google.com/store/apps/details?id=info.guardianproject.ripple https://guardianproject.info/fdroid

I'm adding support to this app right now: https://panicbutton.io/ https://play.google.com/store/apps/details?id=org.iilab.pb

This is all code that I wrote, and you can have it under any license you want, including public domain. I waive all my copyright claims to it.

• Select file and attach to secure conversation
• Share file / to application and attach to secure conversation
• Receiving of file on other end (other instances, like current version smssecure, ignores the payload).

Opened a PR because I am not sure if you read posts on closed PR's to discuss the usefulness of such feature. It works pretty well as I believe, including the edgecases when users try to attach and then switch transport mode. Filename addition to de PDU was also a nice one to debug. Well, let me know.

Added option to disable image resizing if your plan allows bigger (sized) images. Also added a slider to change the maximum MMS size. My provider only allows 300kb messages and as the messages unencrypted stay below 280k, encrypted version might sometimes go over 300kb. So I added a slider to configure this limit.

ps. My first ever android development so might have overseen something in the preferences. Let me know, but seems to work fine.

I applied some of the propositions that Android Studio inspector found in Silence. I let you cherry-pick the commits that you want.

For me the more usefull commits are :

• "SDK_INT is never <9 because minSdkVersion 9"
• "Removed unused import statements"
• "[Manual] Missing supercall fix "

I will push more commits on this PR soon.

I hope @BLeQuerrec that you will accept some of the proposals from Android Studio. Let me know what you think about all that.

Based on #287. This PR removes the back button (useless since tapping on the background masks the drawer), re-add the camera button (removed in dbe30cf) and refactor the drawer with a transparent background. Must be merged after #287 and a rebase.

I removed the com.madgag.spongycastle dependency to reduce the number of dependencies of Signal and because it makes a lot of code that is unused.

I added tests for most of the code of class org.smssecure.smssecure.util.Hex

I hope @BLeQuerrec that you will be interested by this PR.

Display notification if app is locked

dc84d124f860e9de2f9f1a5c435897a2b77e5bed introduced a new way to manage notifications for encrypted messages, but it results in no notifications when device is locked (because message is not decrypted yet). This PR displays a notification when device is locked, even if it is an encrypted message.

Fixes #485