Users menu

First steps to review the user-group menu
The User/Group Display items in top menu have not been removed. That will be covered in another PR.

To Test the PR:
 * Log in as a user in only one group. e.g. user-1
   * Add/remove users from the display
   * Use the "Show all users" option
   * Remove all users by de-selecting the group.
* Repeat the same tests with an user in more than one group e.g. user-4
* Add multiple groups to the display.
* Switch to the Group Display (not modified yet)
  * The menu should only display groups.