Restore community examples

[shilman]

Storybook docs had an examples page which was a community-contributed gallery of storybooks. We removed this in favor of /use-cases but people want to see more examples with source code etc. Let's restore /examples but update it to match the new aesthetic.

[dakebl]

For reference:

Components: https://github.com/storybooks/storybook/blob/4c757d05f162925217751bb5d61518c108d0935b/docs/src/pages/examples/index.jsx

https://github.com/storybooks/storybook/blob/4c757d05f162925217751bb5d61518c108d0935b/docs/src/components/Grid/Examples/index.js

Examples data source: https://github.com/storybooks/storybook/blob/master/docs/src/pages/examples/_examples.yml

Is there a design for this @shilman @domyen? Or should it emulate the grid from the old design, as below?

[shilman]

I think @domyen wanted to redesign..