Connects to bluetooth on android. Device plugin

Dependency on device plugin added:
cordova plugin add org.apache.cordova.device
Can now successfully connect to Bluetooth LE UART devices on android.
Can send messages that are up to 20 bytes long, any longer and they get
truncated.

Next up is to add code for iOS, remove debug alerts etc.
The discovery of services should also be moved to scan stage, such that
ONLY UART devices shows up in connect list.