Tightening up cone fundamental generation code

Added options to DefaultPhotoreceptors that will produce the CIE (aka Stockman-Sharpe) 2 and 10 degree fundamentals.

Added a lot of comments about relation between various routines that do similar things.

Added check that FillInPhotoreceptors and ComputeRawConeFundamentals are consistent with one another, and added extra return args to ComputeCIEConeFundamentals and ComputeRawConeFundamentals to allow access to unnormalized quantal sensitivity functions.

Added other miscellaneous comments.

Signed-off-by: David Brainard <brainard@psych.upenn.edu>