Replace functions named get_

[MaximeBouton]

A lot of functions are named get_..., I think we could remove the get in most of the cases to match julia style guides.

Examples:
get_lane -> lane
get_center -> center (arguable, center is a bit too general, we might want to change it to centerpoint)
get_rear -> rear (or rearpoint)
get_frenet_realative_position -> frenet_relative_position
...