Switch wpblogs server to use jquery-wp-content instead of fork at blog.jquery.com-theme

[Krinkle]

blog.jquery.com-theme is effectively a fork of jquery-wp-content.

Proposed:

• Update the fork with the latest "jquery" theme from jquery-wp-content.
• Update jquery-wp-content with the latest blog theme, including missing theme for jqueryui and jquerymobile.
• Add wpblogs to GitHub org settings as hook recipient.
• Write wpblogs puppet code to support jquery-wp-content next to current provision.
• Switch first one, https://blog.jquerymobile.com, to use jquery-wp-content.
• Switch https://blog.jqueryui.com to jquery-wp-content.
• Switch https://blog.jquery.com to jquery-wp-content.
• Simplify wpblogs puppet code to remove unneeded abstraction and improve reuse.
• Archive repo at https://github.com/jquery/blog.jquery.com-theme.

@supertassu Are you aware of aspects of jquery-wp-content (specifically, the "next" branch) that would make it difficult to use for the blogs? E.g. things that perhaps the blog fork has stripped out that might pose issues?

The main thing I can think of is the multi-site aspects, but we've weeded those out on for the new wpdocs servers where we don't use multi-site WordPress, so I suspect it'd be fine, but curious what you think.