Responsive and choice to change the main theme

Link to the responsive.css file, div tags added to make some content
not-100%-width on large screens and js file that changes the theme
Revert "Responsive and choice to change the main theme"

This reverts commit c0b7150318928035863b325acf3cbf9b95a0208b.
Revert "Revert "Responsive and choice to change the main theme""

This reverts commit aabc4718ba6dbd28e2b57a3d47df3151a8cc2415.