Color Management: `colorspace` not parsed properly in some places

[kwokcb]

A few things found while reviewing colour management support. Could be more.

1. The default value of "none" is not supported. It is being tested as a color space for shader generation.
2. Surface shader node creation does not consider inheritance of colorspace (uses getColorSpace() vs getActiveColorSpace()).
3. Shader translators and texture baker also do not consider inheritance. Also includes using getActiveColorSpace() even at document level I believe if there are include files.