Code Review #4131
Use length of 8 for all redefined vehicles and current wagons
As discussed, we should use length 8 for all redefined vehicles and current wagons, just like in opengfx.
Other new vehicles and wagons can use alternative lengths in the future.
This does mean that the lev 3 and turbotrain 8bpp sprites need to be reworked as they are not visually optimal at length 8.
Feature #4131: Improved 8bpp pixel art to work with 1cc after resize to 8/8