An experiment about drawing an isometric cube that can be edited live in
Inkscape.

The code exploits the fact that Inkscape layers are just groups, so cloning
a whole layer enables some interesting editing capabilities to Inkscape.

Inspired by:
    http://jeroenhoek.nl/articles/svg-and-isometric-projection.html
    https://github.com/jdhoek/inkscape-isometric-projection