Layer Property: Size Scale

[GlenDC]

It would be nice if a layer option can decide how big (and thus how much triangles) the scaling of the trixel-side is. Right now we could concider the default to be 1'.

If the scale would be `1/2' than the triangles would be twice as small and thus there would be twice as much trixels available on that layer.

In order to keep the trixel-layers nicely interlined we would want to keep the scaling factors, multiples of 2, so that it will always nicely fit.