WooCommerce Google Analytics Pro 2.0.16

* Fix - PHP notices if events are inactive
* Fix - Update remaining pre-WooCommerce 3.0 incompatibilities for order tracking

* Fix - Ensure tracking when a customer provides a billing email on checkout is backwards compatible with WooCommerce versions earlier than v3.0

* Feature - Adds checkout options to most Checkout Behavior steps for additional data tracking
* Feature - Improve full site tracking to remove the need for a general tracking Google Analytics plugin
* Tweak - Improved Checkout Behavior funnel support
* Fix - Ensure "estimate shipping" event is always tracked
* Fix - Show only GA property names instead of all views when connecting to a GA account
* Fix - Ensure variation SKUs are used for add to cart events rather than parent SKU
* Dev - Custom event names will no longer be url encoded to respect spaces
* Dev - Global js function renamed to use `ga` instead of `__gaTracker`