More intuitive morphing default case

[guillaume-florent]

There could be a more intuitive way (programatically speaking) to morph the shapes that could be used as a default solution:

• position the morphing vertices based on the bounding box
• move the vertices

[guillaume-florent]

Please see https://github.com/guillaume-florent/PyGeM/commit/7d7d260be77b4d8ca0dec65c917f172cedcad04b for a possible way to do it.