45 remove post data article tag

This is a branch of #36 (pull request https://github.com/Link7/virtual-pages-with-templates/pull/46).

This update includes:
- removal of the post id from the `<article/>` tag
- added option to toggle (on/off) hiding of the post ids - see form `Virtual Pages and Templates Settings` form - Hide ID. Default is disabled. When this is disabled, it will not remove the post ids from the source when viewing a virtual page, hide otherwise.
- unit tests