Private Group List UI
This MR implements the UI for the list of private groups.
It reacts to three types of events to refresh the displayed data:
* new group message received
* private group added
* private group removed
Missing from final implementation:
* entering groups
* adding new groups
* reacting to a future group dissolved event
* actually removing a dissolved group



Closes#660
See merge request !335
Fix NPE when stopping KeyAgreementTask, improve thread safety
This branch fixes#696 and improves the thread safety of the camera code, mostly by adding @UiThread annotations and occasionally by moving stuff onto the UI thread that might have happened on other threads before.
Closes#696
See merge request !345
All text that can be generated by users will show emoji from the
shipped sprites.
For all messages and posts, the custom emoji keyboard is now available.
This also disables menu actions rather than hiding them and thus
closes#677
Included is a fix for a regression that was not showing the keyboard
automatically in forums and thus
closes#676