Allow saving interfaces and crosslinks plots as PNG, SVG, PDF

[p.shah.lab@…]

Want to be able to save these histogram and graph plots to a file to get better quality than a screen shot.

[Tom Goddard]

Done.

Added a "Save Plot As..." context menu entry to the interfaces chain and residue plots and to the crosslinks histogram and network plots. Clicking on the plots shows the menu. The save dialog allows saving as a PNG image, an SVG (scalable vector graphics) file, or a PDF file. The saved plots match the window appearance on screen. The resolution is set to 300 dpi (for png and pdf) and a border padding of 0.1 inch is used. These are parameters of the matplotlib Figure.save_fig() method documented here ​https://matplotlib.org/stable/api/figure_api.html#matplotlib.figure.Figure.savefig

I did not make an equivalent command because if more than one plot is shown I do not have a good way to say which plot you want to save. Maybe the title could be used but that may not be unique. Or the number of the plot based on the order created. These are pretty clumsy. But with no command there is no way to change the dpi and padding parameters. Future enhancement could be to add a command or add those paramters to the Save dialog.

[Tom Goddard]

A related ticket #6823 asks for more control of crosslink histogram axes ranges and bin size.

[Tom Goddard]

Menu entry was added to daily build which will eventually become ChimeraX 1.5. It is not in ChimeraX 1.4.