Add basic avatars and gravatar
Modularize get(), async getAvatar, avatars @ usermgmt

And other small improvements
Add unittests & check filetype in setLocalAvatar()

TODO: Fix OC_Image->mimetype(), it always returns "image/png"
Load avatar from path, if one's provided
Improve styling & enable avatar-upload at personal page
Have /avatar.php as a central avatar-point
Show avatar on personal.php always (except if avatars are disabled)
Use avatar.php in user-management
Refactor newavatar.php and show (for now) an alert on problems when setting new avatars
Have a fancy uploadavatar button
Several improvements

- Don't use gravatars default avatars
- Use "profile image" instead of "avatar"
- Use <p> instead of tables
- Ease updateAvatar()
Actually return something in \OCP\Avatar
Deny access for non-users and add a (not-working) override button
Clean up and prepare a bit for custom default avatars