* Adds a color matrix layer to GAGS
* Fixes default row value
* Passes along the last viable icon for color matrix use
* Removes stray nocache reference
This standardizes how values are read from the json for greyscale layers so that error handling can check for some additional things:
No extra keys in the json that are unknown
No missing keys that a layer needs to work
Values are the expected type for that key
A variety of error messages have been added for various ways the json can be malformed and should hopefully provide good feedback for anyone working with greyscale configurations.
