Add versioned page feature

Add the functionality of displaying the right page version based on the version selector value. It should either select the associated versioned content or display inherited content. Also, the source of the content should be displayed.

1. create the dropdown version selector UIX
2. create the template for the WebHome of a page, which redirects to the sub-pages based on the value of the version selector
3. create a listener which will create the WebHome page (with previous template) and sub-page for the current selected version (with the BookPage object). This will need to work only in a book, and if creating a new WebHome for a page (neither for the hidden sub-pages, nor Versions/Variants space, nor versions/variants pages)
4. create a UIX to display if the page content is inherited or not. If inherited, provide a link to create the current version sub-page