Large re-org of the manage currencies system

This PR extracts 3 new controllers, plus one service from what was
the ManageCurrenciesCtrl.  We have now added the AddGatewayCtrl, the
GatewayListCtrl and the GatewayListItemCtrl.  The added service is named
Gateways and is used to actually manipulate your trustlines and wallet.
```gateway.domain``` in href.