Add functionality to save and restore recently used Emojis

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

Closes #559

Closes #553

Closes #455

Clicking the plus in the toolbar open the `CreateBlogActivity` which
allows the user to create a new blog. Only the first identity is
considered, but support for more identities can be easily added later.

The actual list of blogs in the My Blogs tab will be done in the next
commit.

Will currently fail at runtime; requires a public key and a server onion.

also run setting the default preferences in a background thread

Closes #184