Adds experimental support for `relation_types` and `relation_senders`
fields for filters.

* Remove some unused functions

* get_room_events_stream is only used in tests

* is_exclusive_room might actually be something we want

SYN-287

This requires that HS owners either opt in or out of stats reporting.

When --generate-config is passed, --report-stats must be specified
If an already-generated config is used, and doesn't have the
report_stats key, it is requested to be set.

setup_test_homeserver function in utils.

SYN-47 #resolve