Meshdata update

Some modification in meshdata structure and an example with qt backend to generate, cone, cylinder, sphere and arrow


I'm OK with you for th moment, but for example in the future, you have a mesh with index=None for verts and face. If you want shrink the mesh it's necessery to get verts and faces with index=faces. For face it's very easy i'm OK.

If you want i suppress this possibility ...