This is just a first rough implementation.
A real UI designer should look over this.

Add functionality to save and restore recently used Emojis

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

This allows for swiping left/right to read other posts by using
a ViewPager.

This hasn't been done as a separate activity, but with
fragments, so both can share the `BlogPersistentData` without
needing to reload it.

Closes #428

This commit lays the groundwork for #415

Show system notification for successful introductions