update some participate pages to use location and contact includes

[solon]

• Refactors some of the participate pages by extracting common content (location & contact info) as shared includes.
• Includes a few additional minor copy tweaks left over from #197

How it works

For any pages that use the participate layout, you can now add either or both of the following key/value pairs to the front matter of the page:

location: westbeth
contact: sfpc

These includes then get added to the end of the page when it's generated.