added number of entities count to control panel
added convient accessor method for bodies in Jello.World
added number of Jello.Bodies to debug panel
added getter and setter LiquidSystem in Layer
add convenient method to get number of particles in a fluid system
use setter to assign sample fluid system
added number of particles to debug panel
refactored occurence calculation in debug menu panel
refactored method applyGravitationTo in Jello.World