Google Maps: Detect if required API is enabled and alert the user

[AlexGStapleton]

Recent changes to the Google Maps widget now allows us to validate which API libraries are enabled for the user-supplied API key. We should check for the required libraries and, if possible, conditionally check for optional libraries based on the users SiteOrigin Google Maps settings.

The following API libraries are required:

• Maps JavaScript API
• Geocoding API
• Places API

These are optional:

• Maps Static API
• Directions API