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.  
This would be more readable broken into an intermediate variable like

```javascript
var offerFromTx     = this.offerFromOfferCreate(tx);
var offerProperties = _.pick(offerFromTx, 'account', 'sequence');
var affectedOffers  = this.getOffersAffectedByTx(tx, 'CreatedNode');
var offerFromMeta   = _.find(affectedOffers, offerProperties);
```