Upload user / spekaer picture instead of gravatar

I'm submitting a ..

• [ ] Bug Report
• [x] Feature Request

Current behavior: User profile avatars are only using gravatar.

Expected correct behavior: Allow the user / admin to upload a picture which would be used instead.

Other information: Reason:

• gravatar is not used be every user / speaker and someone doesn't want to use the gravatar service
• It doesn't look very well if a speaker doesn't have a picture.

Here's a very basic set of changes that support both uploaded pictures AND gravatar. I'd consider a full PR, but not sure how supported we want this, and I don't really have the time to clean it up.

https://github.com/snap-cloud/snapcon/pull/45

But it was pretty easy to get to this point.