Replace dashboard locking with 'fullscreen' and 'edit' modes

I didn't think it looked good to always display the nav and toolbar when the dashboard is showing on a big screen. I've removed the locking idea, and replaced it with 'fullscreen' and 'edit' modes. The toolbar and nav are hidden when the dashboard is in fullscreen mode. Clicking anywhere on the screen will take you to 'edit' mode, where they will be shown again, and you can make changes to the dashboard. 

The default `/dashboards/:id` route takes you straight to full-screen mode. I've also added a route for `/dashboards/:id/edit`, which puts the dashboard in edit mode. This let's you set up your dashboard PC to just load the fullscreen dashboard whenever it restarts. Toggling between 'fullscreen' and 'edit mode' will automatically update the URL in the browser.