Rearchitect to use include files instead of submodules

Rather than having submodules, and to avoid landing new users with the confusion of "I just enabled the module but nothing happens", the meta tags should all be handled via include files per meta tag (or per group of meta tags); this would also have the side effect of being able to enable/disable meta tags site-wide via checkboxes (and possibly variables) rather than having to enable/disable modules.