Fix special members for http classes
Stream generated JSON.
Optimize pathfinding operations (RIPD-537):
* Calculate and cache Account hashes without holding locks.
* Fast hash-based path element comparison.
* Use emplace instead of find/insert
Also report mismatched built ledger
Ticket issuing (RIPD-368):
* New CreateTicket transactor to create tickets
* New CancelTicket transactor to cancel tickets
* Ledger entries for tickets & associated functions
* First draft of M-of-N documentation
[WIP] Ticket tests