new vehicle upgrading system

- vehicles upgrade can only be done in auto shop and require knowledge of automechanics

- upgrading cost parts according to its level

- vehicle upgrade in individual aspects : engine (speed) , armor , storage , fuel capacity , color

1) engine : three levels of speed 

                v1 applicable to all vehicle types

                v2 applicable to light and medium vehicles only

                 v3 applicable to light vehicles only

2) armor : v1  adding body armor to vehicle - applicable to all vehicle types

               v2 adding spikes to wheels and plow - applicable to medium and heavy vehicles

                v3 adding gun turret (applicable to certain types of vehicles only as military truck )

3) storage : increase number of storage slots by +1

      maximum no of slots is 9 in heavy vehicles and 8 in light and medium vehicles

4) fuel capacity : v1 , v2 , v3

5) color of vehicl