use qtreactor so twisted is driven by qt main loop

aboutToQuit signal is not raised anymore with the qt4reactor.
So we are calling all cleanup callbacks from the quit function.
catch reactor not running error
fix a segfault when stopping the reactor

this particular way of invoking the run method in the reactor
was giving trouble under some conditions.
switching to runReturn makes it work.
Merge remote-tracking branch 'kali/feature/use-qtreactor2' into develop