Make GCM re-registration failure notification based.

// FREEBIE
rollback to appcompat v20

v21 appears to just not be ready for production given the bugs.
// FREEBIE
Don't completely disable GCM.

// FREEBIE
Updated translations.

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Bump version to 2.3.1

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The future is the other direction.

// FREEBIE
Add callback method parameter to axolotl decrypt functions.

// FREEBIE
Guard against fragment disappearing before callback.

// FREEBIE
Do thread trimming as JobManager job rather than AsyncTask.

// FREEBIE
reorder window feature requests in MediaPreviewActivity

ActionBar is initialized in a different way by AppCompat v20 compared to
ABS or v21 even...
// FREEBIE
fix for ringtone selection with android-support-v4-preferencefragment