Add ProgrammingGroup & ProgrammingGroupMembership

* User can create programming group with other users for exercise
* Submission is shared in a group
* Also adjust specs

app/controllers/application_controller.rb

@@ -23,6 +23,15 @@ class ApplicationController < ActionController::Base
     @current_user ||= find_or_login_current_user&.store_current_study_group_id(session[:study_group_id])
   end
 
+  def current_contributor
+    @current_contributor ||= if session[:pg_id]
+                               current_user.programming_groups.find(session[:pg_id])
+                             else
+                               current_user
+                             end
+  end
+  helper_method :current_contributor
+
   def find_or_login_current_user
     login_from_authentication_token ||
       login_from_lti_session ||