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.

app/models/post_vote.rb

@@ -81,9 +81,9 @@ class PostVote < ApplicationRecord
     return if new_record? || updater.nil? || updater == user
 
     if is_deleted_changed?(from: false, to: true)
-      ModAction.log("#{updater.name} deleted post vote ##{id} on post ##{post_id}", :post_vote_delete, updater)
+      ModAction.log("deleted post vote ##{id} on post ##{post_id}", :post_vote_delete, updater)
     elsif is_deleted_changed?(from: true, to: false)
-      ModAction.log("#{updater.name} undeleted post vote ##{id} on post ##{post_id}", :post_vote_undelete, updater)
+      ModAction.log("undeleted post vote ##{id} on post ##{post_id}", :post_vote_undelete, updater)
     end
   end