Updates to revenue, session recording, autocapture, etc

This release packages up changes and improvements to several subsystems:

• The long-deprecated mixpanel.people.track_charge() method now only prints a console error and no longer sets a profile property or produces any other change. The old version of Mixpanel's Revenue analysis UI has been replaced by a newer suite of analysis tools which don't depend on profile properties (see https://docs.mixpanel.com/docs/features/revenue_analytics).
• Autocapture click tracking properties now include page height and width.
• Session recording now stops when mixpanel.reset() is called.
• New init optionapi_extra_query_params adds support for appending arbitrary query string params to tracking requests (useful for non-standard proxy setups)
• The API of the Feature Flagging system (under development) has been revised
• Whale Browser is now detected automatically