Fix it so that when a forum topic is deleted, all posts in the topic are
deleted too. Also make it so that when a forum topic is undeleted, all
posts in it are undeleted too.
Before when a topic was deleted, only the topic itself was marked as
deleted, not the posts inside the topic. This meant that when a spam
topic was deleted, the OP wouldn't be marked as deleted, so any
modreports against it wouldn't be marked as handled.
Also change it so that it's not possible to undelete a post in a deleted
topic, or to delete the OP of a topic without deleting the topic itself.
Finally, add a fix script to delete all active posts in deleted topics,
and to undelete all deleted OPs in active topics.
Move html_data_attributes definitions from models to policies. Which
attributes are permitted as data-* attributes is a view level concern
and should be defined on the policy level, not the model level. Models
should be agnostic about how they're used in views.
