LinTrain Code

Made the context header variant-specific so that feature tests work
Shuffled memory allocations - there's not really any "non volatile", it's
system config
Added a command to set the mapping of optical detectors to track polarity
Configuration of detector types and mappings in boot block of ARB

Placeholder for new design command station

First pass at code for the PIC on the booster boards. There are some issues
with the build system at the moment.

Two versions of a DCC power booster design:
- a block detector version with four blocks
- an auto-reverser with four opto detectors to trigger polarity change

Added a Python module to communicate with the new command station and present
the same interface as the kernel driver parallel port version

Improved the button ordering on the encoder throttle
Make target to program opto detector with PICkit2 / pk2cmd

Minor documentation and error reporting improvements

Implemented control of loco speed from cabs - the original version acted on
write to a member variable but that's hard in pure Python so use a proper
method. Also removed the undesirable dir -> sign -> dir conversions.
Report errors on accessory command requests and only update the layout GUI
with turnout direction if the request succeeded.
Simplistic controls for static accessories such as building lights
Better accessory naming in dummy mode
Use the XtrkCAD "SWITCHMOTOR" objects to pair turnouts to decoders.
Cope with XtrkCAD's use of "TURNOUT" objects for settrack curves
prog.py:
Hide CV29 bits that are unsupported by the specified decoder (where known)
Support for the new LED accessory decoder
Added a couple of Hornby decoders to the list
Some Python3 fixes

Corrected a capacitor value, added some non-value values
Added a template for a laser-cut and folded chassis

Added a new accessory decoder with eight outputs for LED lighting only.
Ported operations mode CV access to the "light" decoder
Typo fix in the decoder notes