This checks that the domain given to `DomainSpecificString.is_valid` (e.g.
`UserID`, `RoomAlias`, etc.) is of a valid form. Previously some validation
was done on the localpart (e.g. the sigil), but not the domain portion.

This is mostly factoring out the post-CAS-login code to somewhere we can reuse
it for other SSO flows, but it also fixes the userid mapping while we're at it.

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