Enable individual upload of avatar as e.g. png or jpg

[rhofer]

Besides the gravatar.com integration, it would be great to allow individual upload of a picture to be set as avatar (similar to e.g. github or gitlab user profile settings)

1. navigate to ../accounts/profile/#profile of your weblate instance
2. In section Your avatar provide a file dialogue to upload an avatar from your local disk
   • provide and enforce size limits (e.g. pixel size or in kB)
3. Store uploaded picture in database (not in local file system as e.g. media)

Fallback: in case there is no individual picture uploaded, still use gravatar.com as fall back.

In relation to #2964 this would also help to identify a desired user when mentioning in comment function.

[nijel]

I think it should be stored in the file system same as we do with other things (for example screenshots). I currently don't see any benefits in putting this into database. Weblate will require filesystem for forseable future and in case this is going to change, migrating images to database is pretty easy.

[nijel]

When touching this part, it should be made more flexible:

• Using avatars from third-party services we use for authentication, many of them do provide it (see https://stackoverflow.com/a/33161313/225718)
• Upload of user provided image
• Fallback to Gravatar or Libravatar (see Revive Libravatar support #2155)

I think the workflow should be:

• Upon registration whatever is available is used (in order: from the authentication provider, Libravatar, Gravatar)
• User can choose out of avatars from available providers (for example in case he has more authentication methods having avatar)
• Additional option for user uploaded avatar

[rhofer]

Sounds good to me!