"Open Recent" filelist is cluttered with imported image files

Migrated (and condensed) from https://bugs.launchpad.net/inkscape/+bug/1807544

Steps to reproduce:

• use Inkscape >=0.92 in a normal workflow for a period of time
• during this period, import external readable files into Inkscape and export to other formats
• after this period, File > Open Recent...

What happened?

File > Open Recent… menu is cluttered with imported and exported files beside files opened and saved in Inkscape.

What should have happened?

Inkscape should include in that menu only files created in Inkscape and not imported/exported files (behaviour exhibited in versions <0.92). Any extraneous files should be excluded.

Inkscape Version and Operating System:

• Inkscape Version: 0.92
• Operating System: --
• Operating System version: --

Additional Notes and Comments:

• Add a file-type filter option in Preferences > Interface after "Maximum documents in Open Recent" for Open Recent…: ☒ Only record SVG files

• Add a new Import Recent… option that tracks imports/exports, and restrict Open Recent… to open/save operations.

• What users expect from that functionality is, in essence, «I'll open the file I was working on yesterday». That is not generally the case for a PDF file, which tends to be the product of a finished job.