Social login

@nockertsb I had to rewrite the history on master since the private keys for twitter and facebook were on there. I moved the two commits you made to a new branch and did not make any modifications. I'll do a review and tag you when I'm all through.
While it's all the same, typically gradle using single quotes`':AndroidSocialNetworks'` rather than double. Also project dependencies are typically listed at the top of the dependencies section. You don't need to change this, just an fyi.