Major update to Particles class, see description.
Major update to Particles class, see description.

- Added the capability to add, handle and remove spring points and
gravitation particles. On each update() spring and gravity will be
calculated and applied for each of the registered spring points and
gravitation particles.

- Fixed bug in 'getHeading' where return was missing

- Added comments for each method

GorillaBus/PhySim,GorillaBus/Vector,GorillaBus/Vector,GorillaBus/PhySim