Ledger test

https://ripplelabs.atlassian.net/browse/RIPD-432

@JoelKatz @vinniefalco 

This is still somewhat of a WIP, but it is time to get the bulk of it onto develop, get some experience with it, and see where we go from there.
I honestly have no idea.  This code was stolen from here: https://github.com/ripple/rippled/blob/develop/src/ripple/app/consensus/LedgerConsensus.cpp#L1043-L1065