Add functionality to save and restore recently used Emojis

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

This implements a generic `TrustIndicatorView` with a `setTrustLevel()`
method which updates the drawable according to the `Author.State`.

Closes #78

Includes parallel improvements to Bluetooth key exchange UI.

Closes #179

UI was transferred into XML files
and lots of redundant code was deleted such as the custom CodeEntryView.

Closes #33