Better fix for actions with both dont_notify and tweaks

Don't add notifications to the table unless there's actually a 'notify' action

Overlay the push_rules_enabled map for users

Overlay the push_rules_enabled map for users, otherwise they won't be able to disable server default rules.

Make LRU caching tree-based so subtrees of the cache can be invalidated cheaply.

Use new invalidate_many cache invalidation to invalidate the event_push_actions cache appropriately.

Only fetch events for rooms and receipts

Reduce number of calls to get_unread_event_push_actions_by_room

This reverts commit d7265977.

SYN-606: Peeking does not wake up /events

Cache dns lookups, and use the cache if we fail to lookup servers later

If a real user attempted to first peek into one room, and then another,
their room event stream would not be woken up for events in the later
room.

Remove member event rule as per SYN-607