Style Pack: Custom fonts, colours overridden in the preview

[laurelfulford]

In the preview, if the styles define different fonts or colours, they override the custom fonts and colours in the Customizer preview.

This is because, in the preview, the style pack styles are enqueued via JavaScript, and at the very end of the header. Any styles that come before it are overridden.

I'm not totally convinced we need to include colours/fonts in the style packs, but this would be a nice thing to fix.

Steps to reproduce:

1. Navigate to Customizer > Style Packs, and pick Style Pack 1.
2. Navigate to Typography, and set up a custom typeface.
3. Note it's not previewing.
4. Navigate to front end; note the style pack and typeface is correct.
5. Navigate back to the customizer - the font will not be wrong.