Remote instances are now dereferenced when they post to an inbox on a GtS instance.
Dereferencing will be done first by checking the /api/v1/instance endpoint of an instance.
If that doesn't work, /.well-known/nodeinfo will be checked.
If that doesn't work, only a minimal representation of the instance will be stored.
A new field was added to the Instance database model. To create it:
alter table instances add column contact_account_username text;
Inbox POST from federated servers now working for statuses and follow requests.
Follow request client API added.
Start work on federating outgoing messages.
Other fixes and changes/tidying up.
