Merge pull request #737 from ay8s/master

Update Buffer SDK submodule to include v1.1.2
Add bufferShouldShortenURLS option
Add link shortening methods before presentation of the Buffer Sheet
Add requiresShortenedURL, also add ability to turn off Buffer Sheet shortening via config.
Update SDK to 1.1.3

Adds support for disabling link shortening.
Also resolves some issues with link shortening accessing the UI from another thread.