Invited Users Table

* the toolbar and well from the orphans table has been split off into an `invitations_table` layout
* the invited users table also makes use of this layout
* there is a scope to find users who haven't accepted their invitation
* a link for the invited users table has been added to the admin-only Users dropdown
* the invited users table allowed invitations to be resent, and it displays how long ago the last invitation was sent