Add option to NOT show error bars in fits with errors

[gutow]

Currently if fitting is done with weighting by error the error bars are shown on the residuals and the fitted data plots. It would be nice to be able to turn this off. It can be done manually by editing the code generated by the fit GUI as follows:

The error bars can be removed, while still accounting for them in the fit, by deleting error_y_type="data", error_y_array=Yerr where they appear in the scat= statements.