Add User#timeline_posts
Make PostFetcher and UserFetcher raise better exceptions.
Move the upserting of posts from JSON to PostUpserter.

Also, simplify JSON processing by not blindly importing `domain` and `slug`; instead, these will be in inferred from the provided post URL. We're now just checking this URL to have the same host as the source URL used to fetch the JSON, trusting individual nodes not to much up their own data. :-P
Actually, do copy the remote post's GUID from provided JSON.

Reasoning: a post's URL can change (due to permalink-slug-style titles changing, for example), while the GUID must never change, so the two may, in fact, be different from each other.
Truncate referenced GUIDs. I know, it's ugly.
Fix (?) font weight on post author names.
More feeble attempts at fixing the styling problems.

I would test this locally using xip.io, but unfortunately my fucked up excuse for an Internet Service Provider is blocking it, and I can't be bothered/don't want to reconfigure all of my fucking devices to use Google DNS. Fuck.
Styling bugs were caused by viewport setting. RIGHT.
Fix wrapping/mobile styling of main navigation.
Minor styling update.
Render replies to posts using their received Pings.
Track, display and distributed number of replies.
Also serve number of replies in JSON. Duh!
Only show real replies as such.
Add Post#type and Post#data, allowing custom post types.
Update AppSignal gem.
Update jBuilder gem.
Update compass-rails and related gems.
Update CoffeeScript gems.
Temporarily disable Turbolinks until we figure out why it's breaking Chrome's form handling. :(