Scope and purpose

Fixes #3479 as part of Foundation cleanup.

I have gone through the Foundation 5 documentation, and identified components we are not using in the codebase. Some components are not used in any form, while two components (Split- and Dropdown Buttons) are currently unused, but we might want to utilize them.

I added removal of Split- and Dropdown Buttons as a separate commit, and leave the decision of removal up to the reviewers. There are multiple usages of dropdowns in the codebase, but they are all using div or a tags for the trigger, and as such don't take advantage of the styles.

See #3479 for a full list of components and where to find them.

This pull request

• Removes all unused Foundation component stylesheets
• Removes all unused Foundation button component stylesheets

Contributor Checklist

• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• This pull request is based on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file