Visible object check, TopoShape and Mesh support

Implemented visible object check by loading the .FCStd file as a zipfile
and then loading its GuiDocument.xml, from:
https://github.com/danielfalck/freecadweb/blob/master/examples/upload/drawit.py

Also implemented tessellation support for TopoShape and a for a Mesh,
inspired by:
https://github.com/danielfalck/freecadweb/blob/master/examples/springmaker/exportWebGL.py

Modified spec, separated it nicely.