Cleaned code before attempt at doing Ewald's summation.
Half-way implemented Ewald's summation with the incredibly bad
assumption that the reciprocal contribution is zero(!)
Minor bugfixes. Added test that fails on periodic boundaries.
Fixed bug in test which made it fail at boundaries.
Set cells to a size that does not cause (as much) growing energy with
time.
Added force communication between processors to be able to enable
Newton's third law here too.