Add: Tracking Preference Expression APIs

[da2x]

Widely supported:

Navigator.doNotTrack

No implementors:

Navigator.removeTrackingException()
Navigator.storeTrackingException()
Navigator.trackingExceptionExists()

Deprecated (but implemented in Edge and IE):

Navigator.confirmSiteSpecificTrackingException()
Navigator.removeSiteSpecificTrackingException()
Navigator.storeSiteSpecificTrackingException()
Navigator.confirmWebWideTrackingException()
Navigator.removeWebWideTrackingException()
Navigator.storeWebWideTrackingException()

https://www.w3.org/TR/tracking-dnt/