Qt-DAB-3.11-Beta

Travis CI build log: https://travis-ci.org/JvanKatwijk/qt-dab/builds/619673083.
As it turned out, the 3.1 version gave serious problems on some windows systems, while a report on the RPI stated that the quality of the synchronization was less than that of the 2.7 version.
The 3.11 version is based on the 2.7 version, with a rewrite of the control and GUI handling part, such that all buttons and combo boxes of the 3.xx GUI are working.

The 3.11 version is tested - i.e. running for some hours - on an RPI 2, RPI 3, Linux x64 and Windows 10