legacy.py rewritten to use new device class interface

Updated TODO list for the next phase of work on device_classes branch ...

Specifically re-testing samples, then pushing OO classes up into app.

More design on the tx/rx and air_interface pipeline

Documented requirement for a simple persistent data store for the Registry

Initial design for enhanced persistent registry done

Started to flesh out device classes proposed interfaces

Started to flesh out design thinking of device classes

Done a requirements and design pass of the device classes idea

Started a doc to spec and design the device classes