Fix bugs, use new viewmodel to load stops

Summary:
Fix T1185

Update the NearbyStopsFragment type, cleanup MQTT on disconnect.

Rename .java to .kt

Create ViewModel to load stops that are in the map bounding box.

Test Plan: Do stuff.

Reviewers: valerio.bozzolan

Reviewed By: valerio.bozzolan

Subscribers: valerio.bozzolan

Tags: Libre BusTO

Maniphest Tasks: T1185

Differential Revision: https://gitpull.it/D128