New API draft

Mostly for discussing before the new shared API (iOS + OS X) is finalized
Rename `XCDYouTubeVideoClient` into `XCDYouTubeClient`
API: Give the possibility to cancel the video information retrieval operation
Rename `getYouTubeVideoWithIdentifier` method into `getVideoWithIdentifier`
Remove the +[XCDYouTubeClient sharedClient] method
Add language identifier initializer and @property to XCDYouTubeClient
Move XCDYouTubeVideo initializer into a private header
Use xcodebuild + xcpretty instead of xctool
Use `set -o pipefail` for xcodebuild + xcpretty
Upgrade project settings for Xcode 5.1
Split responsibilities between different classes

* XCDYouTubeClient gets the data from the YouTube API
* XCDYouTubeVideo parses the data
* XCDYouTubeVideoPlayerViewController now just uses the client
Pass the URL response to the XCDYouTubeVideo initializer
Use the response URL for better error diagnostics
Remove the `IPHONE_SIMULATOR_CLASS` hack
Test `XCDYouTubeClient` instead of `XCDYouTubeVideoPlayerViewController`
Add unit test for using XCDYouTubeClient on a non-main thread
Make sure that XCDYouTubeClient works on any thread
Remove check for main thread

Now that XCDYouTubeClient supports starting an operation on any thread this check becomes redundant.
Add stream URLs to -[XCDYouTubeVideo debugDescription]
Move error related constants into XCDYouTubeVideoErrorDomain