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

Add functionality to save and restore recently used Emojis

Update emoji and add new categories based on AOSP's XML file

Closes #307

Show system notification for successful introductions

This now handles progress bar and empty view itself.
With this commit, it also scrolls down on layout changes like when
keyboard is opened.

properly notify the view adapter of dataset changes
in order to avoid invalidating the entire dataset when not absolutely necessary.

This change also shows unread messages in a different color,
so users do not fail to notice delayed messages.

It now uses conversation bubbles in alternating colors
and vector drawables to indicate message state.

The conversation bubbles have been taken from Telegram
and can be replaced by a UX designer later.

This commit also addresses #9, because message text can
now be selected and copied. This is done by using

    android:textIsSelectable="true"

which only works for API level 11 or higher.

If we want copy and paste on lower API levels,
additional measures have to be implemented.

and fix message divider background for lower API levels.