Track and Sessions storage

Refine UI behavior.
Store current track and current session.
Move current session to persistent sessions on stop.
Remove persistent sessions on push.
Capture orientation and acceleration changes
Save the current session in memory, not in local storage

Otherwise performances drop, and the app cannot keep up with the events
generated.
The drawback is, if stop is not clicked, the recorded session won't be
persisted.
Prepare server to receive push request from collector