To bring the UI more in line with the proposed design in T54653 for the "Add Drivers" popup panel (NOTE: this is separate from the "Drivers Editor", in previous commit!), this commit adds a new panel - "Driven Property" to the Drivers Editor UI. This basically duplicates the "Active F-Curve" panel (with less options) to make it easier to see at a glance which property the Drivers Editor is showing you.