Potential to add EX-Turntable API command

[peteGSX]

Right now there is no specific DCC-EX API command to control EX-Turntable. There is the diagnostic <D TT vpin steps activity> command for testing and tuning, and the EX-RAIL MOVETT(vpin, steps, activity) command that can be used as part of a ROUTE or VIRTUAL_TURNOUT, but that's it.

Post v5 (PORTX_HAL) release, we can see if it's worth implementing a specific API command and a broadcast feedback, along with a way of requesting the list of possible positions with names so a throttle can maybe create a visual turntable dialog.