Added a global scaling ratio.

- The ratio changes the whole dots-per-centimeter.
- The screen now provides the dots-per-centimeters.
- The screen controls the ratio.
- The mmToFontSize takes the ratio as argument to also scale the fonts.
- A new screen state is added to allow configure the screen ratio from
the renderer actor.
UIList now has a scroll indicator.

- Also made UIrenderUtils more modular.