Fix error when running synapse with no logfile

Fixes 'UnboundLocalError: local variable 'sighup' referenced before assignment'

register some /unstable endpoints in /r0 as well

Code_style updates

Fix port script

We changed _simple_update_one_txn to use _simple_update_txn but didn't
yank it out in the port script.

Fixes #2565

Correctly wire in update group profile over federation

PEP8 fixes

E741 says "do not use variables named ‘l’, ‘O’, or ‘I’".

what could possibly go wrong

Fix a logcontext leak in the media repo

Updates to ID checking

Remove pointless create() method

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.

... because the spec says we should.

Factor out a common function for checking user ids and group ids, which forbids
capitals.

It just calls the constructor, so we may as well kill it rather than having
random codepaths.

Add config to enable group creation

Enforce sensible group IDs