Fix battery element add/remove events handling
Fix battery element add/remove events handling

Battery element was removed when A2DP profile was disconnected. Also,
it was not created when RFCOMM D-Bus endpoint was updated. Now, the
battery level indicator element should be visible as long as its value
is set in BlueALSA service.

Arkq/bluez-alsa,Arkq/bluez-alsa,Arkq/bluez-alsa