Fix FilteringStore.get_user_filter to work with postgres

Implement third party identifier invites

Amalgamate _filter_events_for_client

Encode the filter JSON as UTF-8 before storing in the database.

Because we are using a binary column type to store the filter JSON.

Update the v2 sync API to work as specified in the current spec.

Remove unused room_id arg

Bounce all deferreds through the reactor to make debugging easier.