We know the users are joined and we can explicitly check for if they are
ignoring the user, so lets do that.

Fix bug where pusherpool didn't start and broke some rooms

Since we didn't instansiate the PusherPool at start time it could fail
at run time, which it did for some users.

This may or may not fix things for those users, but it should happen at
start time and stop the server from starting.

Fix up user_ip replication commands

Separate federation servlet into different lists

Fix caching error in the push evaluator

Initialising `result` to `{}` in the parameters meant that every call to
_flatten_dict used the *same* target dictionary.

I'm hopeful this will fix https://github.com/matrix-org/synapse/issues/2270,
but I suspect it won't. (This code seems to have been here since forever,
unlike the bug, and I don't really think it explains the observed
behaviour). Still, it makes it hard to investigate the problem.

Increase default cache size

Improve the error handling for bad invites received over federation

Prefill forward extrems and event to state groups

Cache macaroon parse and validation

Turns out this can be quite expensive for requests, and is easily
cachable. We don't cache the lookup to the DB so invalidation still
works.

Use an ExpiringCache for storing registration sessions

This is because pruning them was a significant performance drain on
matrix.org

Make workers report to master for user ip updates

Batch upsert user ips

Reject local events that don't round trip the DB

Fix up indices for users_who_share_rooms