formulate wall forces as Vector2
removed optimization of Material caching
added materialIndex as a construction parameter for Materials
made getColor deterministic
made datGui local instead of a System's attribute
added datGui switch for using surface tension stub
added alternative fluid implementation
moved surface tension implementation to Simulator class
added getter for the number of Materials
added damping factor to datGui of Materials
added damping factor to surface tension implementation
calculate stress tensor
changed Grid Node opacity
added uscio function to Simulator
added viscosity attribute to Material
finished first iteration of the surface tension implementation