New Feature: multi-page pdf

Created by: tobstac

Problem description

Psy-plot support a range of output formats including pdf. However, every panel needs to be exported in a single file.

Expected Output

It would be preferable to be able to select panels and export them to a multi-page pdf. It would be even better, if the actual export does not happen when the panel is selected for export, but as a final step. For example, if I prepare several panels and realize with the last one that I forgot something in all the others, I could simply add the information to the still accessible panels, instead of having to reproduce all of them again.