Added a gravity modifier.
The scaling of domains and gridpoints are changed. Instead of accepting
a scalfactor and a vector of orientation it now accept a scalevector. A
new modifer for a constant velocity at the boundary is added.
Changed functions for boundary scaling.
Misc changes.
Added damage in the particle class. Damage is updated in the update
function and is accessed through 'getDamage()'
Added non-optimized contact forces.
Added option for an entime equal to the integrators endtime.
Added option for using the integrators endtime as a modifers endtime.