Use Gravatar for user avatars

This dynamic configuration parameter configures the use of the Gravatar service.

• When set to On, Comentario will try to fetch an avatar image from Gravatar for each registered or logging-in user. For federated users (those registering via Google, Facebook etc.), the identity provider avatar will be tried first.
  It also enables the use of Gravatar during import (e.g. from Commento or WordPress).
• If set to Off, Gravatar won’t be contacted.