This expands the current shadow-banning feature to be usable via
the admin API and adds documentation for it.
A shadow-banned users receives successful responses to their
client-server API requests, but the events are not propagated into rooms.
Shadow-banning a user should be used as a tool of last resort and may lead
to confusing or broken behaviour for the client.
We forgot to set the password on the subscriber connection, as well as
not calling super methods for overridden connectionMade/connectionLost
functions.
