replace Like Button send button option with share button option

The new Facebook Like button replaces the send button option with a share button option. 

[Facebook Developers December 11, 2013 blog post announcing full availability of new Like Button](https://developers.facebook.com/blog/post/2013/12/11/full-availability-of-new-like-and-share-buttons-and-flexible-width-for-embedded-posts/).

Update links to Facebook developers site in settings and code comments.