Widgets / Add privileges panel

Migrate privileges panel to Ext.js. Same features as previous one with group filter support. Available for both metadata and batch privilege update.

Thanks Florent who did most of the work !

![widgets-privilegespanel](https://f.cloud.github.com/assets/1701393/1130394/d9476434-1ba5-11e3-80eb-f392bc8f7853.png)