Included xx and yy moments of inertia of the chassis. Made model visuals closer
to the correct value and made it so the .dae used the correct scale already
so the file model.sdf doesn't need to compensate for it anymore.
Included 2 new models, road and cross_road which are an alternative to the
previous road models which couldn't be edited easily since they were set manually
in the world.world file. Also included a my_world.world file with a cleaner look.
Updated the make file so it can be run on x64 systems as well.