add schema.org properties to the breadcrumb...for now (see msg)

add 'itemprop="breadcrumb"' to the "breadcrumbs" element on the category and post pages via _includes/category_breadcrumbs_partial.html and _includes/post_breadcrumbs_partial.html. some breadcrumb content is hidden on the mobile view...currently researching if that's ok.
add schema.org properties to "#main" tag sitewide via the 3 _layouts
change primary containing content element from "div" to "main"