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
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
@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.
