Integrate into WAI site

[SteveALee]

There a few new Jekyll parts that make up the design Guide and these have to be added to the WAI Website.

• config.yml updates for collection definitions and collection defaults
• standaloneresource update for sidebar contents
• two intermediate layouts for Objective and Pattern pages
• two include "widgets" for [pattern list and pager](https://github.com/w3c/wai-coga-design-guide/tree/master/_includes
• a data table of links into cog-usable

I see two main approaches

1) stick everything into the existing theme and global shared submodules / folders. Pro - little new complexity in wai-webite Con - clutter up global resources (poor decoupling) ie Design Guide only includes get added to system theme (though we might be able to abstract them)

2) included from wai-website using folders and links Pro - explicit and minimal use when needed (wai-website) by using existing Jekyll and WAI website patterns Con - added complexity to wai-website - not shared resources

I favour 2 and am testing it out now.

[SteveALee]

@shawna-slh @hidde Any thoughts?

[SteveALee]

Content available at /coga-dg/supplemental-guidance

In steve-design-guide branch:

• updated _config.yml to remove commented out and non existent media collections
• added the repo as a submodule in _external/resources/wa-coga-design-guide
• added symblink pages/wa-coga=design-guide to wa-coga-design-guide/content
• created directories _layouts and _includes for links to items provided by resource repos
• added symblinks _layouts\objective, _layouts\pattern symblinks, _includes\patterns & _includes\pager
• added symblink _data/design-guide-links
• added symblink content-images/wai-coga-design-guide
• moved all collections into a new _collections directory and updated _config.yml to match
• add symblinks _collections\objectives & _collections\patterns
• updated _config.yml to add defaults for patterns, objectives and pages/wai-coga-design-guide
• updated _config.yml to add the collections to the search

To preview see https://steve-design-guide--wai-website.netlify.app/coga-dg/supplemental-guidance/ for the new style pages and also https://steve-design-guide--wai-website.netlify.app for the usual site contents.

This can be copied for the other supporting docs sections