Baseline fitting, Optionally save spatial calibration in a PV, empty GLOBAL fix.

[mcb64]

Three changes:

• Don't crash if the GLOBAL configuration file is empty.
• Give an option to fit a baseline to the gausian/supergaussian fits.
• Add an Expert Mode option to connect the spatial calibration value to a PV.

[mcb64]

Yes, I've tested it and it seems to work just fine. Thanks!