Parameter to disable override_redirect

Another try making xmobar work nicely with notion :)

This time 'Docked' is no longer a 'Position', but a seperate configuration flag. That makes more sense.

With the previous implementation we noticed the WM and X eating 100% when override_redirect is enabled. This was caused by the following loop:

* windowmanager sends Configure events to place the bar somewhere it likes
* XMobar adds a Reposition event to the event queue
* the Reposition event triggers a repositionWin
* repositionWin calculates the desired location and does a moveResizeWindow

This did not quite deterministically lead to some kind of loop, but often did.

I feel we should not add a Reposition event to the queue on a ConfigureEvent at all. The only reason for this I can think of would be to update the width when the screen resolution changes, but this already seems to be handled sufficiently by also watching RRScreenChangeNotifyEvent events.

Feedback welcome ;)