A lof of devices will simply work anyway even if already paired in
Android bluetooth settings. Discover them by default, but warn the user
if the device is not known to pair correctly if already paired in Android
settings. Allows this warning to be disabled to known working devices.
The refactored DiscoveryActivityV2 does not freeze anymore, even under
maximum scanning intensity on older phones, and seems to not have
introduced any regressions.
- get rid of pre-lollipop BLE discovery (nowadays we support only lollipop and above) and related preference
- get rid of the sequenced BT-then-BLE-scan that wasn't working reliably anyway and was causing a recursion
- add a caching layer for already processed devices (the same device is found multiple times during discovery)
- add a caching layer for device name in GBDeviceCandidate (many coordinators will ask for it, and it's a very expensive operation)
