[GSAS-II] GSAS-II plotting updates

[Toby, Brian H.]

I have made some changes to GSAS-II plotting recently, so that now, as refinements are performed with powder data, the plot of the fit is updated after each cycle of refinement. After the refinement, all open plots are updated, if the code for that plot is has update capability included, and plots that depend on refinement results are closed if they are not updated. I think the ability to see what is changing as the fit progresses is a significant improvement.

It has become clear that getting this to work introduced some bugs that depended on what plots are open before the refinement and what tree item was selected when refinement/sequential refinement was started. However, as of GSAS-II version 3962, the logic for updating of plots after refinement has been reworked considerably and has been tested fairly extensively. 

My hope is that there will not be any more bugs with this latest set of changes, but if you do encounter one, please make a note of what plot tabs were open before the refinement and what tree item and what plot was displayed when you started the refinement and send me a GPX file, so that I have some hope to reproduce it. 

Brian