Some UI enhancements

* Add user link to top_nav for admins or masquerading admins
* Add cancel masquerade to top_nav for masquerading users
* Add name of collection to collection items page
* Add link to edit collection on collection items page
* Changed Add Admin to Add User
* Moved Add User button to top to on user index match style on item index
* Moved New Collection button to top of index like on Items and Users Index