The Styles API section of the Mapbox API Documentation site now lists Traffic Day v2 and Traffic Night v2, so this change adds those styles to all the places where styles are listed.
Also switched iosapp and macosapp to unversioned style factory methods since MGLStyleDefaultVersion is no longer applicable for all styles.
Undeprecated the unversioned style URL factory methods in MGLStyle for consistency with the Android and Qt SDKs. Added warnings about using them with the runtime styling API.
Refactored mbgl::util::default_styles to track different versions for different styles.
Upgraded from v9 default styles to v10 wherever the developer expects to get the latest and greatest, as well as in a couple tests where it may be beneficial to ensure that we can handle a two-digit version number in the style URL.
