This also means that the template now has optional parameters, which will need to be documented somehow.

As per https://github.com/matrix-org/matrix-doc/pull/1692

As per https://github.com/vector-im/riot-web/issues/7168#issuecomment-419996117

Fix handling of rejected threepid invites

Fix exception in background metrics collection

Fix exception handling in fetching remote profiles

We attempted to iterate through a list on a separate thread without
doing the necessary copying.

Fix bug when invalidating destination retry timings

Fix error handling for missing auth_event

Fix error when logging incomplete requests

If a connection is lost before a request is read from Request, Twisted
sets `method` (and `uri`) attributes to dummy values. These dummy values
have incorrect types (i.e. they're not bytes), and so things like
`__repr__` would raise an exception.

To fix this we had a helper method to return the method with a
consistent type.

Avoid reraise, to improve stacktraces

Fix lazy loaded sync with rejected state events

Fix exceptions when handling incoming transactions

In particular, we assume that the name and canonical alias events in
the state have not been rejected. In practice this may not be the case
(though we should probably think about fixing that) so lets ensure that
we gracefully handle that case, rather than 404'ing the sync request
like we do now.

 Add a five minute cache to get_destination_retry_timings

Rewrite the dockerfile as a multistage build: this means we can get rid of a whole load of cruft which we don't need.