Allow importing only specific languages / subsets

Problem/Motivation

Currently this module will import all available fonts, even if they are specifically for languages not in use on the current site. It would make the import faster and the font selector easier to navigate if the import only brought in fonts that were relevant to the site.

Proposed resolution

Add a field to form at /admin/appearance/font/settings that would allow the site builder to specify a language / subset and only matching fonts will be imported.