Implement toggle switch for ON/OFF EIP button

It looks like it can be done with a little makeup to a slider: http://stackoverflow.com/questions/14780517/toggle-switch-in-qt

We can put the widget both in the main window and the context menu in systray.

(from redmine: created on 2013-06-14, closed on 2013-10-02, blocks #2979 (closed))