The force calculation was using the Burgers vector in the slip-plane
system to calculate the force in the dislocation's local system. This
has now been fixed. It results in an inversion of the graphs generated
so far, so they will have to be corrected in the wiki.
Merge branch 'version_0.0_simulateSingleSlipPlane' into version_0.0_simulateSingleSlipPlane_dislocationDipoleSource