Implement bikes

[in0finite]

Bike is a special type of vehicle.

They need separate game logic:

• they have 2 wheels
• their entering/exiting/sitting animations are different
• drive-by is different
• steering left/right means leaning bike to a side
• they can't go in reverse, but instead have to be "pushed" back

Implementation details:

• add new class Bike which inherits Vehicle class
• this class is added to Vehicle game object, only if it is a bike
• override methods from Vehicle class to apply special behavior