Add functionality to save and restore recently used Emojis

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

Also replace more raster graphics with vector graphics.

Closes #342

Closes #533

This commit addes a combined blog feed that shows all posts of all
subscribed blogs in the order the blog posts have been received.

For now, this commit also hides other blog functionality like adding
additional blogs and browsing individual blogs.

Closes #417

This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.

A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.

Closes #409

It does so by extending the compound view `TextAvatarView` and provides
convienient setters that take care of the required UI changes.
The new badge can also be used to indicate a problem with the forum.

Closes #408

The new activity shows who you are sharing a forum with and who shares a
forum with you. It is accessible from the overflow menu when in a forum.

Closes #398

Closes #399

Also prevents the snackbar from hiding the bottom of the list.

Closes #337

Closes #307

Removes all programatic calls that modify the layout and uses the XML
resource instead.

Show system notification for successful introductions

@color/briar_text_primary is used in a lot of places other than the settings screen - if we want to use grey text in the settings screen we'll need to find another way.

Also fixed some misspelled resource names and included the colours from the Briar palette in color.xml.