[packaging] replace voicecall-core with voicecall-qt5

voicecall-core pulled in voicecall (Qt4)
I could replace it with voicecall-core > 0.4.9 (which is provided by voicecall-qt5)
but replacing with voicecall-qt5 is even better and more consistent
Merge pull request #3 from faenil/patchpackaging

[packaging] replace voicecall-core with voicecall-qt5