proximity: Emit LinkLossAlertLevel PropertyChanged

Emit the PropertyChanged signal when the service detects that a
disconnection has happened.
gatt: Add the service when the connection already exists

When the device is already connected, we should only add the service
reference to the list of connected services, so it can be disconnected
later.
proximity: Fix not emitting the signals for the Reporter
gatt: Fix make distcheck

We should include 'uuid.h' from lib/.
doc: Add persistency info for proximity ImmediateAlertLevel
doc: Add persistency info for proximity LinkLossAlertLevel
proximity-api: Improve description for ImmediateAlertLevel behavior