Clarify which attributes require link to a Wheel

[petrvanekrobe]

Some GDTF attributes need a Wheel + WheelSlots for best function. Clarify attributes which require it.

[petrvanekrobe]

Currently, Gobo(n), Prism(n), Color(n) are enforced by the Builder. #222

Add:

Requires/Support a wheel: yes, no, optional
Requires/.. a wheel slot (index): yes, no, optional
Requires... a filter
Support Emitter
Support ColorSpace
... Gamut

[petrvanekrobe]

Fixed by #300