mod actions: fix messages to use consistent format.

Fix mod actions to use the same message format everywhere.

Before mod actions were formatted in various inconsistent ways:

* "deleted post #1234"
* "comment #1234 updated by <user>"
* "<user> updated forum #1234"
* "<user> level changed Member -> Builder"

Now all mod actions consistently use this format:

* "deleted post #1234"
* "updated comment #1234"
* "updated forum #1234"
* "promoted <user> from Member to Builder"

This way mod actions are formatted consistently with other actions on
the /user_actions page, where everything is written as "<user> did X".

Also add a fix script to fix existing mod actions.

test/functional/post_votes_controller_test.rb

@@ -286,7 +286,7 @@ class PostVotesControllerTest < ActionDispatch::IntegrationTest
         assert_equal(0, @post.up_score)
         assert_equal(0, @post.votes.active.count)
         assert_equal(true, @vote.reload.is_deleted?)
-        assert_match(/#{admin.name} deleted post vote #\d+ on post #\d+/, ModAction.post_vote_delete.last.description)
+        assert_match(/deleted post vote #\d+ on post #\d+/, ModAction.post_vote_delete.last.description)
       end
 
       should "not fail when attempting to remove an already removed vote" do