Mission Editor: Option to darken map to make flightplans more readable

[twistking]

Very small and simple request:

When editing complex flightplans/routes in ME it's sometimes not easy on the eyes. Especially when editing routes for neutral coalition forces, which are light grey. Would be nice if we could temporarily darken the map, or have another option to make units, waypoint and routes stand out more visually against the map background.