LinTrain Code

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