Add additional ad spots to theme

[laurelfulford]

This issue is to track the potential need for additional ad spots in the Newspack theme:

There are spots ads can be added without editing the theme, like below the content and at the top and bottom of the sidebar.

Ads can also be added by using widgets, or added to the content area using block we're currently developing.

This leaves spaces outside of the content area, and dynamic pages like:

• Archive pages - like category, tag, author, and custom post type archives; content is currently not editable, as it's all dynamically generated. Will have a widgetized sidebar.
• Blog posts page - similar to the above, the page that shows all of the posts on a site. Content for the most part is not editable; since it is an actual page when not set to the front page, we can update the theme to output the_content before the posts are displayed, but can't edit the post output. Will have a widgetized sidebar.
• Search results - content is currently not editable. Will have a widgetized sidebar.
• 404 page - uses a template with static content; can't be edited via WordPress.
• Image/attachment - all page content is dynamically generated, so can't be edited via WordPress.

... and the header and the footer.

For the dynamic pages, if we can't hook into things dynamically, we could manually add hooks to the theme.

For the header and footer, potential spots include above and below the header, and above the footer.