Implementing new single.php template

Does the following:
- implements the 'single.php' template as built for WCIJ, including some basic CSS for the layout and font sixing
- preserves the older Largo-style template as the "classic" single template and applies some CSS overrides to maintain the classic layout instead of the new one
- offers a theme option to use either the "normal" or "classic" template for all posts
- sets the aforementioned option to 'classic' upon upgrade from <0.3 to this version of Largo, so as to preserve existing layouts.