Fix: multiple volumes can be added to the SliceViewer now
Integrated 'color-ramp' feature for vertical curtain visualization
Added button to navbar, which allows drop down menu of navigation items when resolution of screen is small (e.g. mobile devices)
Changed handling of views within a layer
Renamed 'GlobeRenderer' to 'VirtualGlobeViewer'
Adapted 'VGV::removeLayer' to handle multiple views per product