Add basic avatars and gravatar

config/config.sample.php

core/img/defaultavatar.png

core/templates/layout.user.php

lib/avatar.php

lib/public/avatar.php

lib/templatelayout.php

settings/admin.php

settings/ajax/setavatarmode.php

settings/js/admin.js

settings/personal.php

settings/routes.php

settings/templates/admin.php

settings/templates/personal.php