Followup task to T54653 to work on implementing the workflow changes proposed.
(Note: This is currently a lower priority item than fixing bugs to get 2.8 into a usable state for Spring team. But, I'll be working on this when I get time).
There are the following sub-tasks:
* Create operator for "Open Drivers Editor" functionality.
* Basic opening functionality
* Filtering support to get driven property under mouse at the time the "active" driver
* Eyedropper support for clicking in 3D view and getting menu of common properties to drive, based on item under mouse.
* Basic object support
* Investigate possibility of bone support too. (NOTE: Last time this was tried, it turned out being too complex to accomplish)
* New persistent floating panel UI for adding and editing driver settings
* Floating panel
* Basic layout
* Driver variable management