export any MIES plot to SVG from context menu

Create a right-click menu option to export MIES plots contained in the SF window, PA plot, data browser, and sweep browser. These plots are inside panels, so the Igor menu doesn't support SVG export. 


```
SavePICT/O/E=-9/Win=SweepFormula_plotsweepBrowser_graph#graph0 as "SBPLOT.svg"
```