Remove fetched results controller from posts view.

Whatever promise this once showed has never been realized. We can fetch cached
posts on our own quite easily, and we get the posts back from the client when
we scrape new ones.
Remove table view-like API from AwfulPostsView.

Having removed the fetched results controller, there's no need for this
overcomplicated API.
Move HTML generation entirely out of AwfulPostsView.

The delegate must now be able to generate the whole page of posts at once.

This broke the "previous posts" action's keeping the scroll position the same
while revealing new posts at the top. The fix is introducing a dedicated method
to prepend posts (as opposed to using the now-defunct UITableView-like API). A
happy side benefit is that there's no longer any KVOing of the scroll view.

In addition, the PostsView.mustache template now includes the current font
scale and highlighted username settings, so there's no need to update them on
load. A FontScale.mustache template now shares the font scale style between the
PM view and the posts view.
Delete unused -[AwfulPostsView reloadAdvertisementHTML].
Outfit AwfulPostsView with some WebViewJavascriptBridge.

All the basic JavaScript function calls are now handlers on the bridge.

* Remove the pointless -update... methods from AwfulPostsView. Just update them
  in the setter, if appropriate.
Mention implicit includes in JavaScript.
DRY up JavaScript between PM view and posts view.

Renamed util.js → common.js and added everything that's used at least twice.
Delete unused method -advertisementHTMLForPostsView:.
Move rest of AwfulPostsView to WebViewJavascriptBridge.
Can register most handlers immediately in private-message.js, no need to wait for DOM to load.

It's just the click event that calls a handler that we need to wait for. Though
I imagine given how things are structured, we don't even need to do that.
Posts view is no longer a scroll view delegate.
Don't cache post template in posts view.
Tidy up AwfulPostsViewController a bit.

* Inline some short methods that are only used once.
* Delete -setThread:. Thread should never change.
* Simplify composition delegate completion handling.
* Reorder a few methods.
Redo AwfulPostsViewController API.

* Consolidate various stages of loading process back into single method that
  takes a flag parameter for whether to go beyond the cache.
* Render "end of the thread" message in PostsView.mustache.
* Stop scrolling back to the top when reloading the page.
Move most of AwfulPostsView into AwfulPostsViewController.

Just about done moving everything out.
Fix jumping to post when loading awful:// URLs.

Includes Leper's Colony and links to other posts.
Fix bungled posts view JavaScript.

* Awful.highlightMentions is now highlightMentions.
* Inserting undefined to the DOM does not work well.
Goodbye AwfulPostsView.