X6: Use MATLAB-compatible channel keys.
X6: Use MATLAB-compatible channel keys.

Avoids having to re-write the channnel keys for MATLAB. And avoids MATLAB
mangling of the channel names when modifying Instruments.json.

Plourde-Research-Lab/PyQLab,calebjordan/PyQLab,BBN-Q/PyQLab,rmcgurrin/PyQLab