Webinterface

Completely replaced old web interface. Several changes to Sia HTTP API, fixes and restructuring.

The initial commits produce a mockup application, later commits add a scripts directory that contains data bindings to update the application with actual data.

The interface has two global modules, ui and controller. The controller controls polling the go http server, while the ui takes the data and translates it to the interface. The ui also has a method to add listeners for events (e.g. "stop-mining") that the controller can bind to to send requests to the server.