Navigation details

* only show navigation scrollbar on hover, when needed, to be less obtrusive even when you have a bunch of apps
* simplify noise (immense file size reduction of ~1MB! sorry for the iinitial big noise), also apply to user menu and header, fixing #1576 
* double speed for user menu slide. Default is 400, and 200 looks way snappier – maybe also good to use for the settings slideup in the rework @Raydiation 

Check it @arkascha @Raydiation @karlitschek