Room version upgrade support

Improve comments, get old room state from the context we already have

This test stubbed out some stuff in a very weird way. I have no idea why. It broke.

Make Docker image listen on ipv6 as well as ipv4

Currently just creates a new, empty, room, and sends a tombstone in the old
room.

... to save passing it into `_send_events_for_new_room`

Signed-off-by: Cédric Laudrel <dek@iono.me>

we're going to need this for room upgrades.

Currently when fetching state groups from the data store we make two
hits two the database: once for members and once for non-members (unless
request is filtered to one or the other). This adds needless load to the
datbase, so this PR refactors the lookup to make only a single database
hit.

Add config option to control alias creation

fix race condiftion in calling initialise_reserved_users

Autocreate autojoin rooms

there's really no point spinning up two separate jobs for these.

I don't think we ever use this, and it slows things down. If we want to use it,
we should just do so on a couple of builds rather than all of them.