Styleguide for PR #7

So, finally it's there :D
I hope I'm now conform to your style guide. Relating to my last pull request I made some additional changes, mainly improving the window handling.
Now there are the problem with Mission Control left (I don't now why I thought I fixed it, maybe it was on Mavericks, I'm now on Yosemite) and a minor issue (namely a window of the app get focused when opening popover).
I also added the Transiency monitor for hiding the popover when clicking on other menu items. I didn't add the dummy menu (it had no effect for me) and the content size API (I use autolayout). You can merge them back.