Change module description to use a paragraph tag

I'm not sure this should be a heading, I think it's just body text.

Update the styles to match.
Switch module styles to be mobile first
Add right margin to the filtered list status text

This stops the 'x' to remove a filter from touching the text to
the right of it.
Update unpublished warning styles

With feedback from @henryhadlow.
Add prototype warning to page-per-thing
Merge pull request #636 from alphagov/bugfix-prototype-banner-page-per-thing

Add prototype banner to page-per-thing