GT html export should have a way to specify pages to skip

[botwhytho]

Currently all pages in a Lepiter database are exported. Pages that don't appear in the table of contents page don't appear in the navigation but they do get exported to the output directory. This is not necessarily bad as one can have a Drafts page that doesn't appear in the TOC that has links to WIP pages one may want to share with others for feedback.

There should still be a way to through overriding a method and/or providing a command line argument skip certain pages from being in the output directory at all.