Use aspect maps and add ability to use alternate light config (#422)

[mb-m]

Idea to use a map to control the pins set for the different signal aspects, instead of just straight RED->redpin, AMBER->amberpin, GREEN->greenpin. There is a main map which does this and then an alternate map which may do anything. In the example, we use red -> amber/green -> green, which is the Deutsche Bahn signalling resolution (where physical signals are used rather than in-cab).

This rewrites the LED section of the RMFT2::doSignal(), making it use the aspect map for even the features of merging red and green together for amber and the high-is-off setting. It adds 2 new automations: SIGNALA and SIGNALAH to allow the use of the alternate maps.

[mb-m]

Hi Maintainers, please note this is a work in progress and hasn't actually been tested as per the issue it references (#422). I'm mostly interested in what you think of it at this stage - am I barking up the wrong tree?