This adds a little button per vehicle class to the station window which opens a list of all vehicles that have this station on their schedule.
As side effect this gets rid of some global variables.
This adds no functionality, but is a stepping stone for future improvement (like 16bit order indices) and is easier to read.
This changes preserves binary compatibility wrt savegames.
- reduce to 2 sizes (*DParam64 for 64bit values, *DParam for the rest)
- use inline functions instead of macros
- add assert()s to check for buffer overruns