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/helpers/users_helper.rb

@@ -26,7 +26,7 @@ module UsersHelper
   end
 
   def disabled_roles(user)
-    current_user_role = current_user.highest_priority_role
+    current_user_role = current_user.role
 
     # Admins are able to remove the admin role from other admins
     # For all other roles they can only add/remove roles with a higher priority
@@ -38,7 +38,7 @@ module UsersHelper
                               .pluck(:id)
                        end
 
-    user.roles.by_priority.pluck(:id) | disallowed_roles
+    [user.role.id] + disallowed_roles
   end
 
   # Returns language selection options for user edit
@@ -52,6 +52,11 @@ module UsersHelper
     language_opts.sort
   end
 
+  # Returns a list of roles that the user can have
+  def role_options
+    Role.editable_roles(@user_domain).where("priority >= ?", current_user.role.priority)
+  end
+
   # Parses markdown for rendering.
   def markdown(text)
     markdown = Redcarpet::Markdown.new(Redcarpet::Render::HTML,