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.
The code in this `makePayment` method seems so very similar to the code in `makePayment` above, and (to a lesser extent) `createOffer` and `cancelOffer` too.  They also use what we seemed to decide before is the wrong way to fill a transaction.

Isn't there some way to reduce this code duplication?