Provide ability for admins to manage user organisation membership & admin rights

- Required overwriting a bunch of base code to slot in the handling
- Admins are shown with yellow text in their organisation label

locale/en_US/messages.php

@@ -40,6 +40,8 @@ return [
         'ADMIN_COUNT'         => '# Admins',
 
         'SELF'                => 'My Organisations',
+        'MANAGE'              => 'Manage Organisations',
+        'ASSIGN_NEW'          => 'Assign to organisation',
 
         'NAME' => [
             1 => 'Organisation name',