A colloction of 3D format converters, step->wrl, iges->obj/mtl, step->obj/mtl

Originally by twlostow

A converter based on openCASCADE, which accepts *.step or *.igs and exports *.wrl.

I created a CMakeList to compile the project with windows/openCASCADE 6.3.1.

Problems TODO:

1. If the step is exported from UG and some of the faces are colored, then the un-colored faced are not exported. However, if all faces are uncolored, the output is OK; This shall be a logical problem in the code because all entities are loaded according to the verbose information of occ.
2. *.igs loading is unstable. There may be empty output.
3. This may not be able to deal with compicated models.