It is a common pattern to have a list with an empty view and a progress bar.
This commit introduces a custom BriarRecyclerView and uses it for the
contact list.
No more manually hiding and showing empty views and progress bars is
necessary when using the new BriarRecyclerView instead of RecyclerView.
Please note that this conflicts with !44 at the moment and needs to be
implemented for !36 once merged.
Closes#198
The button hides itself when you scroll down the list of contacts
and shows again when you scroll up.
To properly color the button, the accent color has been defined.
It uses the same color as the action bar (primary color).
I leave it to a UX designer to adapt the color scheme.
Please note that the design support library was used.
It includes the app-compat library, so this has been removed
from the `build.gradle` file.
Closes#199
Dev task #52. Known but unverified identities are also supported, but
currently unused. These will be used in future for contacts who've been
introduced but not verified face to face.
