some refactoring for easier development of some other features

theme/templates/base.html

theme/templates/index.html

theme/templates/macros/cards.html

theme/templates/macros/common.html

theme/templates/macros/content_renderer.html

theme/templates/macros/link.html

theme/templates/macros/nav.html

theme/templates/macros/renderers.html

theme/templates/page.html

theme/templates/tag.html