Trading Client Backend - Rev 1

This PR notably adds the Trading service and OrderBook model, used to buy/sell currency.

In addition, there is a temporary "trade" page that will be removed prior to merging with master that is a testbed for functionality.  
The reason the amount isn't a big number is becasue the design for the normalized amount object is to represent the value as a string of decimal digits.

Remember, the whole idea behind this approach is to use plain old javascript objects to represent the normalized form, rather than going with the custom object approach that stellar-lib takes.