General cleanup and minor refactoring.
Renamed NearFarScalar members for consistency, also removed code bloat.
Fixed documentation generation error with @private usage in DrawCommand.
Renamed czm_eyeAltitude2D to czm_eyeHeight2D and storing
ShaderProgram._eyeHeight2D as a Cartesian2 for normal and squared distance.
Defaulting scaleByDistance to be undefined.

Signed-off-by: Alex Wood <abwood@gmail.com>