While the base URL remains configurable, this patch reverts back to using
Gravatar.
We noticed high latency with libravatar and contacted them. They are in the
process of migrarting to a better infrastructure (it's a single personal server
at the moment) so we'll re-evaluate once that has happened.
As for why not leave the default and change it on the meet.jit.si installation,
we don't want to kill their server :-)
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