GRN2-xx: Switch the relation between users and roles to make queries cleaner and faster (#1299)

* First steps

* Fixes in account creation flow

* Fixed most testcases

* more test fixes

* Fixed more test cases

* Passing tests and rubocop

* Added rake task to remove rooms

app/models/ability.rb

@@ -25,7 +25,7 @@ class Ability
     elsif user.has_role? :super_admin
       can :manage, :all
     else
-      highest_role = user.highest_priority_role
+      highest_role = user.role
       if highest_role.get_permission("can_edit_site_settings")
         can [:site_settings, :room_configuration, :update_settings,
              :update_room_configuration, :coloring, :registration_method], :admin