MUMUP-1385: Polish drag and drop

Better styles for dragon drop (lol, check out this site: http://mrcoles.com/dragondrop/)

Due to the annoying incompatibility of bootstrap and jquery ui-sortable, I couldn't get the placeholder background-color to work. But I think there is enough affordance with the box-shadow and tilted box to satisy the user. I think this functionality is not perfect, but it works.

![screen recording 2014-12-08 at 04 03 pm](https://cloud.githubusercontent.com/assets/1919535/5348271/069afc68-7ef4-11e4-86c8-005193a2e9b3.gif)