Fix activity feed (#1779)

* Fix activity feed

Preserve actions after user/repo name change

* Add missing comment

* Fix migration, and remove fields completely

* Tests

models/fixtures/action.yml

@@ -3,10 +3,7 @@
   user_id: 2
   op_type: 12 # close issue
   act_user_id: 2
-  act_user_name: user2
   repo_id: 2
-  repo_user_name: user2
-  repo_name: repo2
   is_private: true
 
 -
@@ -14,10 +11,7 @@
   user_id: 3
   op_type: 2 # rename repo
   act_user_id: 3
-  act_user_name: user3
   repo_id: 3
-  repo_user_name: user3
-  repo_name: repo3
   is_private: true
   content: oldRepoName
 
@@ -26,8 +20,5 @@
   user_id: 11
   op_type: 1 # create repo
   act_user_id: 11
-  act_user_name: user11
   repo_id: 9
-  repo_user_name: user11
-  repo_name: repo9
   is_private: false