Fix setting thread's seenPosts from page of posts.

We were inconsistently setting the thread's seenPosts property, depending on
what was being parsed (HTML or JSON) and whether the server gave us an updated
value.
Codify comment.
Sort posts when parsing JSON.
Fix unread posts and count.

Was setting the thread's seenPosts property before rendering the posts. Not
ideal but this fixes it for now. (Ideally the posts would render the same way
whenever the posts view asks. This way, posts render differently after the
first time the posts view asks.)
Fix un-editable posts when scraping HTML.

Probably also fixed by going to the Settings tab.
Add thread tag "sadev-bugs".
Reload posts when thread's seenPosts changes.

This looked really bad when you had a thread open on iPad, then
swiped-to-delete on the sidebar to clear the unread count. Now the posts nicely
turn unread.

As a bonus, no need to reload posts in -markPostsAsBeenSeenUpToPost: anymore.
Remove useless markingPostsAsBeenSeen property.

This was used to avoid reloading all of the posts in the posts view just
because we were marking some of them read, which would trigger because of the
old beenSeen property on each Post. No more Post property, no need to jump
through these hoops.
Hide Leper's Colony when logged out.
Filter out useless stuff from GitHub Pages.
Reload forums list on appear.

Since we ignore the NSFetchedResultsControllerDelegate calls when we're not
visible, we need to reload when we are visible.
Switch back to forums.somethingawful.com

I don't think the dev.forums redirects worked 100%.

Also switch JSON requests that aren't in production to only use JSON on
dev.forums. While the Forums will simply give us HTML if they don't support
JSON yet, we don't want an incompatible JSON output to go into production and
make everyone crash.
Formatting.
Fix KVO crash.

If a posts view controller's thread changes, we didn't remove ourselves as an
observer, so a new object would inherit the observation and crash.
Remove AwfulPostsViewController#threadID.
Fix KVO leak in AwfulPostsViewController.
DRY up finding/creating a thread by ID.
Extract AwfulPageLast/NextUnread into new file.
Formatting.
Commentary.