Enhancement: Allow drag and drop reordering of TVs in Template TV grid

This is the first attempt to solve the annoying "not-being-able-to-reorder-TVs-by-drag-and-drop"-problem existing since Revo was released (and that functionality existed in Evo), so far it seems to work quite well, but as I'm far from even little skilled with extJS, I don't know if my approach is even a valid one...

Related issues (maybe there are more, but these I could find with a quick search):
#9410 #9698 #5095 #11120 #4592 #11102

with the proposed changes it works like this:
![modx templatetvs dd](https://cloud.githubusercontent.com/assets/445501/3357870/55659818-fad7-11e3-9c62-5b8d1f9d3c13.gif)