Graphics overhault rebase1

[mmatera]

This tries to rebase #635 against mathics 2.2.0.

Resume of that is inside this:

• graphics3d: small fixes for using mp numbers
• tensors: adding transform symbols.
• graphics: a lot of changes.
• Image: Rasterize, using svgtopng from nodejs. This includes the introduction of a module layout, that exposes the interface for rastering. It seems to do more than this, but I do not have clear for what else is it for.