[MJ-46] Profile Image

Makes the following changes:
- Gravatar email field in the user model. On account creation, it is set to the user email address but can be edited in the edit account page. If user has no gravatar image, a default gray user image is seen in its place.
- 20px Gravatar image in topbar
- 100px Gravatar image in initial profile creation form as well as edit account form
- Improved edit account page to prepopulate form fields with the appropriate data
- Test for gravatar url creation

All tests pass.