Merge pull request #86 from morgenroth/Whisper-improvements

Whisper improvements
android-api: Blocking calls removed

Application must wait until the session is connected before executing any calls to the
service. Otherwise the result of the methods is invalid.
android-daemon: Forward ENDPOINT_ID preference to the service process
android-daemon: Remove orphaned variable
android-daemon: Catch SQLException in case of an duplicate entry
android-daemon: Use non-blocking API pattern in the collector service
DTNExampleApp: Use non-blocking API pattern
Whisper: Use non-blocking API pattern
Communicator: Use more obvious declaration of DTNClient.Session
ShareBox: Use non-blocking API pattern
Talkie: Use non-blocking API pattern