Allow hiding UI elements with a URL parameter and fix missing toolbar when exiting fullscreen.

For dashboard displays we need to be able to hide headers and toolbars with a URL parameter.  This change introduces the "minimalui" query parameter that does this.  It also adds listeners for the BigScreen enter/exit events to fix the missing toolbars after exiting fullscreen.

Ultimately it might make sense to move the BigScreen code into a dedicated directive and out of MainCtrl.