Showing user images from gravatar

In the issue https://github.com/epicmonkey/pepyatka/issues/16 I started thinking about adding gravatar to service.

I know noting about javascript, so I'm not sure this solution is correct, but it works on my dev server.

The other thing I want to point out is that I generate md5 from email every time, maybe it should be stored in the redis. I did this solution only because it was simpliers.
You don't need this... that :)