Use card design for generic category landing page

[mDuo13]

Redesign the pagetype-category.html.jinja template to use cards rather than bullet points, for consistency with the visual language of the other pages. The cards don't need unique card-bottom graphics. The left sidebar should still be present on these pages, but they don't need a right sidebar.

We may do a more thorough revision of the pages later to improve the navigation experience, but for now we're just giving them a slight facelift.

[amarantha-k]

Related Issue #2093

[amarantha-k]

Closing this issue as #2093 will address this issue.