Add bottom margin to images on page, blog, and archive pages
Various changes and additions to Customizer options:
* Customizer: Removed Multi-Author Mode option in favor of enabling via Child Theme. Default is disabled.
* Customizer: Compiled Post Excerpt options in into Select drop-down.
* Customizer: Added option for hiding widgets from single pages (default is enabled).
* Refactored author card and site header info code to improve code reuse.
* Refactored single.php code to allow widgets.