Road maps: Display Scale factor

It might be required for different dpi devices to make the scale factor adjustable. This is the same settings as Cruiser/Settings/Display Scale.

In VTM, the setting is:

CanvasAdapter.userScale = 1.2f;

Right now, on my Nexus 7 1920x1200 it looks really nice at how it is, but I haven't tested road rendering on lower-res devices.