add test for add and remove wiki page

[matsl]

What

• Add hywiki-tests--get-page-list-after-add-and-delete
• Set mod time and checksum on file creation

Why

Did an attempt to write a test case that verifies that the pages returned by hywiki-get-page-list when adding and removing pages. I know removing might be something we are working on but it felt that the caching is not perfect. So the test case might not be worth adding in its present state but can be worth discussing. So filing it as PR for review and discussion.