Adds basic sharing to WordPress for iOS from other iOS apps.

Supports drafting a new post with a title, some content, tags, and a URL to an image that
will appear as a link inserted at the top of the post.
Support for base64 encoded images should coinside with the updated media library feature.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into feature/sharing
Clarify what's being logged, and don't use pointers for NSUIntegers.
Merge pull request #1211 from wordpress-mobile/feature/sharing

Feature/sharing