add taxonomy templates

[P-skylos]

• adds taxonomy_list.html and taxonomy_single.html for zola to fall back on when rendering taxonomies
• made it so taxonomy_single.html inherits from section.html
  • I had to wrap the post list and the title in blocks to override them since they refer to the section object explicitly
• added a list_terms macro to the macros file to be used in taxonomy_list.html

[not-matthias]

Thanks for the PR!