Features/new dashboard

Here's the new Backbone.js based dashboard. Currently all views poll for new data every 2 seconds regardless of the interval configured in the `DashboardOutput`. The dashboard should behave correctly with or without configured sandboxes and should detect configuration changes and re-render correctly without reloading the page.

There are a few things that would be nice to have that aren't included:

- Unit and/or integration tests.
- Ability to pause or stop polling for data.
- Config based polling interval.
- Additional information from Filter plugins.
- EventSource based incremental updates.

I'm up for adding those (or anything else) if time permits, but I think that they could wait for a subsequent release.

I have only tested the sandboxes with very limited data. It would be nice to get more interesting data (telemetry?) hooked up with multiple sandboxes to do a proper test.