Ux improvement

Hi, here is a couple of UX improvements I use with your extension.
The improvements are :

* MultiSelect form fields (I use the bootstrap-select component : https://github.com/silviomoreto/bootstrap-select writen by silviomoreto )
* AuthItem names appear in grid view in addition to the description
* AuthItem description appear in assignement grid view
* User filter in AuthAssignement grid view (based on User->username)
* Column filter in AuthItem view (I use the table-filter js https://github.com/hail2u/jquery.table-filter writen by hail2u )