Mock registry store created, auto_create is working

Documented requirement for a simple persistent data store for the Registry

Started to implement device classes code. ...

Simple mocking interface now working.

Initial design for enhanced persistent registry done

Some ideas about device registration added

Method signatures for device classes added

Started to flesh out device classes proposed interfaces

Updated device database comments for MIHO002 device

FSK Transmit coded, ready for test

Restructured switch.py so we have a tx-only test. ...

This is in preparation for pushing the FSK transmitter into radio.c

Implemented a standalone switch exerciser demo. ...

Note this only really works with Adaptor Plus
(unless you seed the directory with your device id's first)

Updated device database

Added rudimentary support for MIHO005 (HOUSE MONITOR) and MIHO013 (ETRV) ...

Fixed bug where eTRV sends an empty JOIN message that crashed the code
Added some extra fields to the CSV to support apparent power for House Monitor
Note: Voltage scaling on house monitor is incorrect.

Removed and tweaked a lot of trace messages to make it less noisy

Improved message decoding. ...

Now builds a dictionary of seen devices.
Monitor FFFFFF messages removed, not needed.
Catches bad payloads and prints a warning rather than crashing.
Accepts and responds to a JOIN command.
Message and value encoders written and working.
Message and value decoders written and working.