Allow configuration of organization (user?) profile pictures without gravatar

[agjohnson]

It's a really bad UX for organizations at least. They should be able to set a nice, cropped image as their org profile picture.

I could see maybe similar for teams? Or at least do a automated avatar with uniqueness for team icons.

And probably also the same for user profile avatars, this would allow us to ditch Gravatar and the external request. It makes sense only if we are already doing this for other models though, Gravatar technically works just not great.

[humitos]

We started added avatars to organizations in readthedocs/readthedocs.org#12254. We should probably do the same for users and teams once that's done. Probably the same applies to projects, too: #536