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.
This is all magic here - particularly since it fails!  What is this constant?  Why should the quality of this constant be `6125895493223874560` - and why is it failing?

If we're going to have more than one test involving non-trivial qualities in future, consider extracting both the 256-bit hash and the quality out as constants, so we can use them in other tests - and the names would serve as documentation as to what they meant.