Fix bugs regarding battery-saving feature

@garvankeeley There are some major bugs regarding #1270:
- manually stopping scan while paused restarts scan on movement (`ScanManager`)
- minimizing app and stopping scan from notification never deactivates location listener (`MapLocationListener`)
- metrics not updated on pause (`MainApp`)
- restarting scan when paused does not update notification (`MainApp`)

Still not sure if this covers all possible problems.