Update CocoaPods to 0.27.1 and fix Podfile.

xcodeproj doesn't need an explicit require anymore, and the ARCHS setting
doesn't need fixing anymore.
AwfulHTTPClient no longer subclasses AFHTTPClient.

Not sure why it ever did, honestly. Nobody needs to know how it gets the info
it gets.
ImgurHTTPClient no longer inherits from AFHTTPClient.

Nobody needs to know.
Use relative paths in Imgur API client.
InstapaperAPIClient no longer inherits from AFHTTPClient.

Encapsulation etc.
AwfulThreadTags -> AwfulThreadTagLoader, no longer an AFHTTPClient.

Hide the implementation details, plus that name always bugged me.
Update to AFNetworking 2.

Everything using an AFHTTPClient needed updating as that class no longer exists.
Formatting.
Show user info in private message view.
Lighten keyboard bar
Add HTMLReader.
AwfulThread.rating is no longer optional; still defaults to 0.
AwfulUser upsert convenience method takes username as well as user ID.

Both are optional, but one of them must be set. In addition, we can update the
unset value.
Use HTMLReader to parse thread lists.
Migrate to XCTest and test HTMLReader-based thread list parsing.
DRY up HTML response serialized operation creation.

Only necessary during the transition. In the end, all HTML responses will go
through HTMLReader.
Fix xctool install on Travis-CI.
Tidy up API for listing threads.
Travis CI script updates CocoaPods before running.
Share Awful Beta and Awful App Store schemes.