May as well do it whenever we parse a Group ID. We check the sigil and basic
structure here so it makes sense to check the grammar in the same place.

POST /_matrix/client/api/v1/rooms//send/a.b.c gave a 500 error, because we
assumed that rooms always had at least one character.

Have all unit tests import from our own subclass of trial's unittest TestCase; set up logging in ONE PLACE ONLY

fix the copyright holder from matrix.org to OpenMarket Ltd, as matrix.org hasn't been incorporated in time for launch.

Add a HomeServer.parse_roomalias() to avoid having to RoomAlias.from_sring(..., hs=hs) - similar to parse_userid()

add in copyrights to everything, not just the synapse subdir, and add a copyrighter.pl whilst we're at it