Feature/treebeard

#### Purpose
This pullrequest replaces hgrid with Treebeard which effects four locations:
- Project overview Files widget uses fangorn (Fangorn is the rubeus of treebeard)
- Project Files page uses a wider implementation of fangorn.
- Project Organizer is revised to work with Treebeard
- folderpicker.js is revised to work with Treebeard. 

In this pull request all functionality should mimic the existing functionality; legacy design and issue fixes are not done in this PR. 
 
#### Changes
- Hgrid is uninstalled from bower and file references are removed. 
- Rubeus is replaced with Fangorn
- Treebeard is installed with dependencies: Mithril is the main one that OSF doesn't already have. It also needs jquery and jquery ui. 
- Add on configuration files are replaced with Fangorn versions. 

#### Side effects
Fixes the folderpicker remembering the picked folder. 
File upload is a major component of OSF so significant edge cases may arise. The functionlity of add ons is tested but can cause unhandled behaviors.