v2.0.0: Switch to GraphQL API for latest version support

[MickeyKay]

This PR drastically simplifies the BFA library, with some key improvements:

• Cuts over to use the Font Awesome GraphQL API for all data, consolidating the previous multiple API calls to a single optimized call.
• Removes the ability to select a specific version, instead defaulting to the latest version always.
• Removes the ability to select unminified CSS.
• Adds the ability to include the Font Awesome v4 shim CSS for backwards compatibility.
• Deprecates a few legacy functions, filters, and args.

This PR is a dependency of the related PR into the actual Better Font Awesome plugin: MickeyKay/better-font-awesome#17