disallow multiple "calibration" operations

[jywarren]

I've noticed that some people may add many redundant and overlapping operations to a spectrum, adding a great deal of overhead which has no analytical function, and which may cause extreme slowness -- for example multiple linearCalibration operations.

For example: https://spectralworkbench.org/spectrums/83225 seems to have over 1000 tags?

While https://spectralworkbench.org/spectrums/83251 has several redundant calibration tags.

I've tried to walk a fine line with /forbidding/ operations which don't make any sense (it's frustrating to have a program tell you not to do something!) but in this case I think we should throw an error rather than let the program run more than one stacked calibration -- it should say "remove the existing calibration to add a new one" or something.