Refactor the post preview html to use the ViewComponent framework. This
lets us encapsulate all the HTML, CSS, and helper methods for a UI
component in a single place.
See https://viewcomponent.org.
Rework post deletion from using a separate page to using a dialog box,
like flagging.
* Add `DELETE /posts/:id` endpoint.
* Remove `POST /moderator/post/posts/:id/delete` endpoint.
Remove `POST /moderator/post/undelete` endpoint. Replace it with
`POST /post_approvals` instead.
Fixes it so that undeleting a post has the same behavior as approving a
post. Namely, it reloads the page instead of just flashing a "Post was
undeleted" message.
Standardize on using `show_deleted: true` instead of `tags: "status:any"`
when rendering thumbnails and we want to show deleted thumbnails.
Also fixes it so that deleted thumbnails are shown when reordering pools
and favorite groups.
