Removed cout in atomType constructor.
Changed onMoved and onRemoved from functions to vector of functions so
that we can have more event listeners.
Fixed so newton's 3rd law is not used on atom/ghostatom pairs.
Added name property on potentials for couting.
Added << operator on system.
Fixed so both debug and nodebug uses a firstKick on first step in
velocity verlet.
Marking cells as dirty when updating ghosts.