Add dialog to change the positions source in-map

Summary:
Change colors of icons

Try clearing cache to avoid OutOfMemory error (to attempt fixing T1222)

Add icon for the bus positions service

Update icons

use activity viewModels

Implement custom dialog and switch positions source (fixing T1347 and T1346)

Improve appearance

Add another status for completeness

Change fonts slightly

Test Plan:
View map.

Put app in background. Re-open map.

Tap bus stop. See arrivals.

Back to map. Click "Change source" icon, close. Do it again 5 times.

Click "Change source" and change it (from Mato to GTFS).

Click "Change source" and change it again (from GTFS to Mato). See realtime stuff again.

See bus lines. Open one.

Reviewers: valerio.bozzolan

Reviewed By: valerio.bozzolan

Subscribers: valerio.bozzolan, Libre BusTO

Tags: Libre BusTO

Differential Revision: https://gitpull.it/D205