[MTR4] EuroTram - Metro do Porto

Added the EuroTram, with Metro do Porto's livery, split by the following models:

• Cab (Foward)
• Cab (Backwards)
• Cab (Foward/Coupler)
• Cab (Backwards/Coupler)
• Carriage (Small)
• Carriage (Normal)
• Carriage (Panto)
• Carriage (Panto/Reverse)

A normal single unit train would have the following consist:
Cab (F) + Carriage (Panto) + Carriage (Small) + Carriage (Normal) + Carriage (Small) + Carriage (Normal) + Cab (B)

A double unit train would have the above consist twice, with the middle cabs swapped by their coupler variants! (You may also switch the pantograph car's position from the first "normal" car to the "last" car)