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

 - target seems to be overwritten between setDevice and startSource
 - deeper debug necessary

To test:
 - VideoTranscoder
 - API-Access from QML

To fix:
 - call of startSource from QML in main.qml on stream button pressed

 - integration of api in qml
 - switching to qt av in progress

 - Support encoding profiles for 720p30, 1080p30, 1080p60, 1440p60