Apply the filter the 'timeline' and 'ephemeral' keys of rooms.
Apply the filter to the 'presence' key of a sync response.

A couple of weird caveats:
 * If we can't validate your macaroon, we fall back to checking that
   your access token is in the DB, and ignoring the failure
 * Even if we can validate your macaroon, we still have to hit the DB to
   get the access token ID, which we pretend is a device ID all over the
   codebase.

This mostly adds the interesting code, and points out the two pieces we
need to delete (and necessary conditions) in order to fix the above
caveats.

Removes device_id and ClientInfo

device_id is never actually written, and the matrix.org DB has no
non-null entries for it. Right now, it's just cluttering up code.

This doesn't remove the columns from the database, because that's
fiddly.

We're about to have two kinds of token, access and refresh

setup_test_homeserver function in utils.

Add logic to map the appservice token to the autogenned appservice user ID.
Add unit tests for all forms of get_user_by_req (user/appservice,
valid/bad/missing tokens)

split the storage and management of filters from the actual filter code
and don't have to load a filter from the db each time we filter an event

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