Fixed bug 1148 : Double deallocation causes crashes during Workrave shutdown

Signed-off-by: Rob Caelers <rob.caelers@gmail.com>
Fixed compatibility with gnome-shell 3.10

Signed-off-by: Rob Caelers <rob.caelers@gmail.com>
Merge remote-tracking branch 'origin/master' into next

Conflicts:
	common/src/GlibThread.cc
	frontend/apps/qt5/src/SizeGroup.hh
	frontend/common/src/SoundPlayer.cc
	libs/input-monitor/src/unix/XScreenSaverMonitor.cc