cleaned up alot of the code by introducing static variables for alot of shared stuff in event class. Also moved some stuff from mesh class to event class since they belonged here in the first place. Fixed bug in temperature fluctuations when no atoms were present in the meshfield. Hard to test whether the new mesh setup works, since it shuffles around the order at which some events are executes (thermostats before or after integrator and so on, since there work on different meshes. Preserving this order seems pointless; should the depth of the meshfield influence the order of events perhaps..)