Add support + examples for working with external components / custom elements / etc

[thescientist13]

• https://www.webcomponents.org/
• Bootstrap
• Others?

[thescientist13]

Did some discovery on webcomponents.org and mostly found that most require bower and HTML imports to work and / or show a tight coupling to Polymer. Looks like there might be a case to source components outside of that repo.

Maybe Bootstrap components would be a better test? Or maybe this repo? https://github.com/origami-cms/zen

Or maybe something of our own!? 💡

[thescientist13]

From Polymer Slack

I would say don't expect lots of 3.0 elements until there's an official release of the Polymer 3.0 elements. It just doesn't seem legit yet imo

[thescientist13]

done https://github.com/ProjectEvergreen/projectevergreen.github.io/pull/19