Send email notifications for missed messages

Implement basic ignore user API

    Remove templates-vector and theme templates with variables instead
    Switch to matrix.to URLs by default for links

Remove templates-vector and theme templates with variables instead
Switch to matrix.to URLs by default for links

Add and use get_domain_from_id

Add some log information at returned replication streams

Add cache to get_user_by_id

Run transaction queue on reactor

Queue events by room for persistence

This ensures that any CPU work that happens doesn't block message
sending.

Reduce database inserts when sending transactions

Add an openidish mechanism for proving that you own a given user_id