Google Fonts Option Type

Instead of the Typography option type, I've build this Google Fonts option type for a project I'm working on. This option type makes it possible to select a Google Font, while updating the font variants and subsets dynamically either via AJAX or JS. Also added to option tree is the ability to fetch Google Fonts, by supplying the API key via 'ot_google_fonts_api_key filter'.

It might be better if this option can be somehow integrated into the Typography option type so we don't have both of them.

Thank!