Reduce database access and improve defaults when setting up avatars.
Review Request #9589 - Created Feb. 5, 2018 and submitted
The avatar registry, when running for the first time against a site
configuration from an older version of Review Board, would attempt to
migrate the gravatar settings over and then save the site configuration
back to the database. When threads spun up, they'd all load their site
configuration and then write it back out, invalidating all their states
and forcing reloads, which was expensive.
The state is no longer immediately saved. Instead, it's just migrated
locally, and that migrated state will be persisted when the site
configuration is next saved to the database.
Saving the avatar settings is also less noisy. We no longer cause
multiple saves to the database and multiple siteconfig invalidations.
Instead, we set all the state up-front and then save it all at once.
Along with this, the defaults are now more reasonable when migrating
from an older version. It used to be that if Gravatars were disabled, we
wouldn't set any default/enabled services, meaning that if people wanted
to enable gravatars, they had a few fields to fill out. We now always
default a migrated configuration over to supplying Gravatars as the
default/enabled services, instead of clearing out the values. This helps
keep things consistent with the behavior used when saving the avatar
configuration in the form.
Unit tests pass.
Tested configuring avatars and toggling defaults.