* Federation: Implement Query Profile API

Implements the server portion of: `GET
/_matrix/federation/v1/query/profile?user_id=...&field=...`

Closes #278
Signed-off-by: NAndrew (anoa) <anoa@openmailbox.org>

* Properly export profile-related structs and fix wording
Signed-off-by: NAndrew (anoa) <anoa@openmailbox.org>

* Check provided user's domain matches our own.