Use latest vanilla Grappelli + Filebrowser versions

Mezzanine uses forked versions of Grappelli and Filebrowser that are getting quite old now. I wanted to have some new Filebrowser features such as Flash-free file uploads (see issue #875), image size presets, as well as a new TinyMCE version.

So I made the necessary changes to get Mezzanine to play nicely with the latest vanilla versions of Grappelli and Filebrowser. This will avoid having to maintain 3 separate projects and concentrate the efforts on Mezzanine itself.

I think I have tested most of the features, and they're working fine (this was mostly template work and Filebrowser debugging). There could be additional cleaning to do (I didn't get the goal of the GRAPPELLI_INSTALLED setting for example). There's also just one thing I couldn't figure out how to solve: in the breadcrumbs menu, there are 2 new arrows (put there by Grappelli) that allow you to open/close all collapsed elements and I couldn't figure a way to integrate it nicely in the current breadcrumbs bar.

Feel free to test and report issues!