Changes for Right-Left Coordinate Systems & Prefixed Mesh Parts with Mesh Name

Mesh.cs:
Removed spaces before and after the # 

StandardMaterial.cs:
If a file is .png, sets alpha transparency

XNAExporter.cs:
1) Added changes to automatically convert from a right to left handed coordinate system.  Maya is right, Babylon.js is left.  This involved changing the winding of the triangles, and negating Z positions & normal.

2) Added changes so that mesh parts had the mesh name prefixed


Also added DeltaKosh's /rl flag and only did transformation if flag was true.