Merge pull request #5 from josiangeldiaz/omniauth

OAuth implemented
Limit OAuth to providers that specify an email

Which should keep the login flow simpler. Also implements enough to
deploy (and test) on heroku.
More robust Heroku deployment

* Unicorn server
* Rollbar error monitoring
* Working email sends
Add avatar urls to users
Clean up the app layout and nav bar
Fix potential performance problems
merged James updates to my fork
removed application.html.erb
added basic styling and modified topic index