Added instant response on rejecting data connection request and fixed bug with resuming listening for connection in NetworkSinkHandler

 - dblclick on playback window toggles fullscreen

 - closing application terminates StreamThread and NetworkSinkHandler gracefully

 - debugging required, crashing after few seconds in CachedStream::answerDataRequest()

 - class is passing all tests

 - tests missing

 - Using Qt Test framework
 - Tests are running successfully