Add Sequential and Series fitting to EngDiff GSASII tab

[DanielMurphy22]

Describe the solution you'd like Add Sequential (use outputs from 1st spectrum as inputs for 2nd, 2nd for 3rd, ...) and Serial (All spectra have the same initial parameter) fitting from the fitting tab to the GSASII tab. Series is already what we currently use.

Additional context Not sure, but it is likely this will have to work with texture grouping. Are there other complex fitting routines that saurabh wants?? Is this something we should coordinate ourselves (say call GSASII many times) or is there sequential fitting in GSASII itself that can do this for us?