Merge pull request #72 from ricardovaleriano/google-sign-in

Add google authentication
Merge branch 'master' into twitter-signin-removal
Merge pull request #74 from ricardovaleriano/twitter-signin-removal

Twitter registration removal.
Merge pull request #75 from ricardovaleriano/uniq_user_per_email

Uniq user per email
Merge pull request #76 from ricardovaleriano/user-merge-tool

User merge tool
Merge branch 'master' into twitter-avatar-promotion