Improve Placer by using a 3D Zig-Zag-Pattern

[Adrodoc]

The current default placement uses a 2D Zig-Zag-Pattern to generate a flat plane for each process and then stacks the planes according to their heigth.
Due to inline processes (#34) it is very likely that there are few but very long chains. In such scenarios the current placement generates very big stuctures, because a process can't use the tertiäry direction.
A better algorithm would fold the plane in a second Zig-Zag-Pattern to reduce expansion in the primary and secondary directions.
Hopefully the new algorithm will also be stable enough to reliably support a max coordinate.