Implement issue #1219: Update the marker line when quassel loses focus

Solves [issue #1219](http://bugs.quassel-irc.org/issues/1219) on bugs.quassel-irc.org.

We now listen for QEvent::WindowDeactivate in the main window. This should pickup on window closing/minimizing/losing focus. We also change view->setMarkerLine() to Client::setMarkerLine which will send an event to the syncher, and eventually arrives at ChatView::markerLineSet, which moves the marker line for us.