Social graph integration

[djwesto]

@GilesGibson mentioned they used to have a function to pre-populate Twitter tweets and Facebook posts with various fields from a node's content. I don't know how this was done and why it went away but it's a powerful method to improve shareability of content and we should either:

• Investigate and reintroduce / fix the existing functionality
• Investigate the various OpenGraph solutions we could replace the existing functionality with