Set up a pattern portfolio

[simonw]

https://www.slideshare.net/nataliedowne/practical-maintainable-css/75

This will be a single page that demonstrates all of the different CSS styles and classes available to Datasette.

[simonw]

I'm going to put this at /-/patterns, which will render a template called patterns.html.

[simonw]

Now live at https://latest.datasette.io/-/patterns