[Suggestion] Bigger limit for motor sounds playing at the same time in train.dat

[NYCTRailer]

As it is known, there can only currently play 2 motor sounds in 1 instance which are #motorP1 and #motorP2 same on deceleration. A bigger limit would make some required motor sounds to be detailed properly.

[s520]

This limitation is discussed in this PR. I intended to remove this restriction with Train.xml, a new format that replaces Train.dat. However, I am undergoing medical treatment and my work is stagnant.