Update font sizes and line spacing.

[DFurnes]

Changes

This PR updates font sizes & line spacing based on new values specified by @lkpttn. It also adds more generous line spacing to wider container elements, and increased spacing between paragraphs.

Screenshots

Here's the pattern library with the old values:

And with the new values:

...no really, they're different! :mag: :eyes:

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For review: @DoSomething/front-end

[lkpttn]

I think this is good to merge in for testing, we may tweak a bit more depending on how it looks on thor/staging.

[DFurnes]

@weerd @sbsmith86 Ready for another review! Added a type-scale() function to tidy up where those numbers come from & one unrelated change to the .heading.-banner pattern.

[weerd]

Nice! Really like the new scale function :dancer: :+1:

[sbsmith86]

Love the type_scale() stuff! looks good to me ;)