Fix group-scheme bug with changing LJ parameters in FE

Fix group-scheme bug with changing LJ parameters in FE

We don't optimize for the case when we have only changed one of charge
or type, so the other vector must always be valid even when it is not
changing. The logic of calling ewald_LRcorrection didn't do this
correctly, perhaps because the construction logic in md2atoms was
unclear.

Changed name, origin and logic for bFreeEnergy to
bHaveChargeOrTypePerturbed to better reflect the correct usage and
meaning. Avoided testing any pointers for NULL - we should use
explicit control-flow constructs.

Fixes #1596

Change-Id: I61172681048075d3022bd6c4b781c6c9153eeadd