New manager design for 2.3

Very heavily based on [this](http://www.edenweb.ie/blog/2014/01/28/modx-redesign-2.3/) and [this follow-up](http://www.edenweb.ie/blog/2014/03/20/modx-cms-design-update/), this pull request contains a fresh new design for the manager for 2.3. Please see the links above for some background on the design decisions, I will attach some screenshots to comments on this PR with some highlights. 

While the changes are mostly contained in the (S)CSS, some changes and fixes required adjusting some javascript files as well. This PR also includes #11397 and was merged with modxcms/develop this weekend so should still be easy to merge. 

The goal of this PR is to get it merged in for 2.3 which will open it up for testing and feedback from the wider MODX community before moving towards a stable version. There are no doubt visual bugs, possible improvements and cross-browser stuff to sort out, which is easiest with more eyes on it.