Added the ability to delete or clear notifications.
* A "Clear all" button deletes them all (with confirmation)
* A "Remove" button on individual notifications (one confirmation per
page load, so you can remove several without too much tedium)
Fix some things regarding private photo notifications:
* When notifying your existing grants about a new upload, only users who
opt-in for Explicit are notified about Explicit private pictures.
* When revoking private grants, clean up the "has uploaded a new private
photo" notifications for all of your pics from their notification
feeds.
Finish implementing the basic forum features:
* Pinned threads (admin or board owner only)
* Edit Thread settings when you edit the top-most comment.
* NoReply threads remove all the reply buttons.
* Explicit forums and threads are filtered out unless opted-in (admins
always see them).
* Count the unique members who participated in each forum.
* Get the most recently updated thread to show on forum list page.
* Contact/Report page: handle receiving a comment ID to report on.
Implement Likes & Notifications
* Like buttons added to Photos and Profile Pages. Implemented via simple
vanilla JS (likes.js) to make ajax requests to back-end to like/unlike.
* Notifications: for your photo or profile being liked. If you unlike,
the existing notifications about the like are revoked.
* The notifications appear as an alert number in the nav bar and are read
on the User Dashboard. Click to mark a notification as "read" or click
the "mark all as read" button.
Update DeleteUser to scrub likes, notifications, threads, and comments.
