There are now quite a few frontend components in the app.
It’s good to have a reference for them to:
- document for developers what patterns are available and how they are used
- check for regressions
- when working on one variation of a pattern you can check that your changes
don’t break other variations of it
- when changing the arguments to a pattern you can check that this doesn’t
change the expected arguments already in use
This commit adds a single page (`/_styleguide`) which has examples of all the
patterns.
