* Add support to upload a picture to forum posts and replies, in forums that
have the PermitPhotos setting enabled.
* New DB table: CommentPhoto holds the association between a photo and a
forum ID. Photos can be uploaded at preview time (before a CommentID is
available) and get associated to the CommentID on save.
* Cron endpoint /v1/comment-photos/remove-orphaned can clean up orphaned
photos without a CommentID older than 24 hours.
* Add "Photo Boards" as a default forum category for new boards.
* Add ability to (un)subscribe from comment threads on Forums and Photos.
* Creating a forum post, replying to a post or adding a comment to a photo
automatically subscribes you to be notified when somebody else adds a
comment to the thing later.
* At the top of each comment thread is a link to disable or re-enable your
subscription. You can join a subscription without even needing to comment.
If you click to disable notifications, they stay disabled even if you
add another comment later.
