Add home links cards to styleguide, used in new docs and new support center

[solepano]

There is a new design for docs home links which is also shared with new support center:

@nkohari has started the implementation on his doc's fork: https://github.com/nkohari/auth0-docs/blob/new-navigation/client/styles/inc/category-card.styl, but since same styles are needed in the support center this should be moved to the styleguide.

Thanks,
Sole

[vctrfrnndz]

Added in 4.7.6