Ticket Support

This is the implementation of tickets, as described in https://ripple.com/wiki/Multisign, which is required for M-of-N work.

A set of integrations tests to check ticket creation, lookup and deletion will be needed and will be pushed into this request as soon as they are done. 
This sentence is sort of tortured (and is also missing a comma).

Perhaps:
"For accounts which are designated as multi-sign, there must be a list which specifies the number of signatures necessary for a quorum, as well as which accounts are authorized."