Fix Impact Category list view actions

[mrvisscher]

This PR fixes an issue where context menu actions in the Impact Category List view failed because they were triggered with a generator instead of the expected list object.

• Closes Can't delete created method #1361

Checklist

• Keep pull requests small so they can be easily reviewed.
• Update the documentation
  • For in-code documentation, please follow the numpy style guide.
  • For user documentation, please update the wiki in
    ./activity_browser/docs/wiki
• Update tests.
• Link this PR to related issues by using closing keywords.

If you have write access (otherwise a maintainer will do this for you):

• Categorize the PR by setting a good title and adding one of the labels:
  bug, feature, ui, change, documentation, breaking, ci
  as they show up in the changelog.
• Add a milestone to the PR (and related issues, if any) for the intended release.
• Request a review from another developer.

[coveralls]

coverage: 54.205%. remained the same
when pulling dabd005 on mrvisscher:method-table-fix
into 5b4b200 on LCA-ActivityBrowser:main.