Add a general setting to consume avatar services
avatar services like https://es.gravatar.com/ are controversial, provide a recognizable image from an email, but at cost of leak all the emails that could provide an avatar to an external service.
In many cases it just interrogates about emails present in public service already gathered by avatar service providers.
Would be great if we can enable gathering avatars from external services at desktop level, controlling if that retrieve should happen only for some emails (users ones) or all emails susceptible of avatar retrieving.
related to gitg#203 (closed)