Parallelization of interaction loops in Law2_..._Capillarity (which is in fact not a LawFunctor handled by InteractionLoop). Moreover adopting the FOREACH iterator for the non-parallel flavour.

Considering simulations of a dense sample with 10000 bodies, executions of capillary Law2 took :
- before change : ~ 1700 s / 100 000 executions, whatever j option (j4 or j1 tested)
- after change : 620 s / 100 000 executions with j4 (only one run tested)

So:
- Law2_ScGeom_CapillaryPhys_Capillarity is now parallelized (thanks to InteractionLoop example...)
- approx *3 speedup is reached from j1 to j4 (better benchmark could maybe have been done)