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

src/Database/Models/User.php

@@ -37,7 +37,7 @@ class User extends UFUser
         /** @var \UserFrosting\Sprinkle\Core\Util\ClassMapper $classMapper */
         $classMapper = static::$ci->classMapper;
 
-        return $this->belongsToMany($classMapper->getClassMapping('organisation'), 'organisation_members', 'user_id', 'organisation_id');
+        return $this->belongsToMany($classMapper->getClassMapping('organisation'), 'organisation_members', 'user_id', 'organisation_id')->withPivot('flag_admin');;
     }
 
     /**