Class 37 option for SEHS MFA services

This pak file adds the Class 37 from West Cornwall Local into the mix for loco selection on services with MFA wagons.
Note: This may not play nice with other substitution mods involving Class 37 and 66. So its advised to remove pak file whenever not required.
37onmfa.pak adds only the WCL37
Pnzdsn37mfa.pak adds the wcl and tvl 37s
In addition Added reskin file for the TVL 37. Generic plain Blue similar to unbranded 37s seen in recent times.