android-api: New DTNIntentService class added

This implementation of an IntentService avoids locking of the main thread
during the registration procedure.
android-daemon: Send broadcast intents only to App with the right permission
android-daemon: Hide ugly error message during session termination
DTNExampleApp: Use new DTNIntentService for all DTN operations

Additionally, a menu item is added to perform a deregistration.
Whisper: Add debug menu item for deregistration
Whisper: Use new DTNIntentService for all DTN operations
Talkie: Use new DTNIntentService for all DTN operations
ShareBox: Use new DTNIntentService for all DTN operations