Add train stop ability to read train group

[marcin212]

I have two groups of trains and one station. When a train arrives, I would like to check which group it belongs to and, based on that, decide what to load into it. Currently, this can only be done by train ID, which means always having to add the train ID to the decider. It would be nice if it were possible to assign a signal to a group or read the group ID, or have signal based on the icons in group name.