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.  
It doesn't matter to me.  The important thing is that the current implementation at /trade exists and is separate from your work on the frontend so I can continue to use it as a testbed for the backend.  If that testbed needs to go to another url thats fine.