support-the-multi-attachmentviewer

[jberends]

Fixes #

Checklist:

• My code follows the pykechain style
  • I added type hinting to all functions
  • I added documentation for all public functions
  • I locally used tox to check for dists and docs errors
  • My code passes the pep8 and flake8 linting checks and no warnings
  • I removed unused imports, using Code > Optimize Imports in PyCharm
  • I used black to format the new code
• I have added tests that prove my fix is effective or that my feature works
  • I committed fresh test cassettes
  • I have proper test coverage (don't decline the coverage of the test)
• I asked another teammate to review the code
• I update the Changelog.md with the appropriate changes.

[raduiordache]

Don't forget the changelog and at least a small test. Although the test will have to be commented out since it will fail until we have that widget.