ptcloud property tweaks

Changed name of class & removed redundant text label as suggested by
Bishop.

Also hiding the has_color property in the UI, since it’s not really
useful. Fading the use_color property in the absence of color data as a
hint that you shouldn’t expect much in the 3D viewport.
spaces & braces

Cosmetic/style changes to more closely match blender coding standards:

— real tabs instead of 4 spaces (oops, editor settings)
— braces where 95% of people expect them
— fully embraced statement blocks, even for one-liners

No functional changes.