Restructure the 'Export' tab

[aalfons]

When we add functionality to export the diagram of the selected mediation model, the Export tab will become very cluttered with inputs and file previews.

We could have different tabs for the different files (model diagram, diagnostic plot, table of results) within the Export tab. The challange is how can we make that look nice and intuitive to use? This is not so easy, because we need separate inputs and outputs for each file type (conditional on whether that file is selected to be exported), but we also need some overall inputs in the tab to select which files should be exported.

What is a good way to implement this? Are there alternatives to using separate tabs within the Export tab?

[aalfons]

Have different tabs for model diagram, table, and diagnostic plot. They have different sidebars to customize the relevant options, but the all show the button to generate the files and to select which file types should be exported.

When first entering the tab, it might be good not to have any customization options. Those are only shown once the preview is generated (for the visible tab).