Media Library [4.0]

Video demo coming shortly.

##### Media Library
1. Browse all the media for the blog, both self-hosted and WP.com
2. Removed duplicated media-adding code
3. All media adding/deleting happens through the media browser (including featured image for posts)
4. Multiselect to delete (there was going to be a feature to add a gallery to your post, to make more use of the mutliselect)
5. Edit media attributes
6. Play videos
7. Handles private blogs (authenticates the download of images/videos/thumbnails)
8. Uses the same resize views/code as before
9. Search by text across title/caption/description, filter by month/year.

##### Known Issues
1. wp.newMediaObject does not accept a date. This means that since WPXMLParserDelegate does not convert the date coming from the server (GMT) to GMT (NSDate automatically uses the device's timezone), the date on the media item is double converted. The visual effect is when adding a media item, the item is not at the top of the list. It appears after any media added from the app within the last X (where X is number of hours offset from GMT) hours. @astralbodies has let me know that there will be a fix eventually at the root to make sure this doesn't happen. The rest of the app's data can send a date in the POST and converts the date to GMT on outbound.

Themes is also included in this branch, due to a decision made months ago. I can decouple themes from this branch at request :)