Push badge counts

[dbkr]

Fixes the 'push notification badge count' part of https://github.com/vector-im/vector-web/issues/469

[erikjohnston]

Rather than abusing SyncConfig it'd probably be cleaner to add a storage function get_receipts_for_room, e.g.:

    @cached(num_args=3)
    def get_receipts_for_room_for_room(self, room_id, user_id, receipt_type):
        return self._simple_select_list(
            table="receipts_linearized",
            keyvalues={
                "room_id": room_id,
                "receipt_type": receipt_type,
                "user_id": user_id,
            },
            retcols=("event_id"),
            desc="get_receipts_for_room",
        )

or possibly using _simple_select_one_onecol

[dbkr]

ptal, at least for the bits you didn't help me write. Have added the index on user_id to receipts_linearized too.

[erikjohnston]

Other than unindenting update_pusher_last_token, LGTM