Coulomb Scattering fully conservative

Coulomb scattering is now fully conservative thanks to the method in
lemos2009small.

The trick was to conserve the momentum and energy of ALL particles
involved in the scattering in each cell.

The substeps in Coulomb collisions have been removed as they are no
longer necessary.

Still some issues with e-i, but I don't know right now.

src/modules/moduleCoulomb.f90

@@ -14,8 +14,6 @@ MODULE moduleCoulomb
     REAL(8):: A_j
     REAL(8):: l2_j
     REAL(8):: l2_i
-    REAL(8):: tauSub
-    INTEGER:: nSubSteps
     CONTAINS
       PROCEDURE, PASS:: init => initInteractionCoulomb
 
@@ -48,7 +46,7 @@ MODULE moduleCoulomb
 
     END FUNCTION H
 
-    SUBROUTINE initInteractionCoulomb(self, i, j, subSteps)
+    SUBROUTINE initInteractionCoulomb(self, i, j)
       USE moduleSpecies
       USE moduleErrors
       USE moduleConstParam
@@ -56,14 +54,10 @@ MODULE moduleCoulomb
       IMPLICIT NONE
 
       CLASS(interactionsCoulomb), INTENT(out):: self
-      INTEGER, INTENT(in):: subSteps
       INTEGER, INTENT(in):: i, j
       REAL(8):: Z_i, Z_j
       REAL(8):: scaleFactor
 
-      self%nSubSteps = subSteps
-      self%tauSub    = tauMin / REAL(self%nSubSteps)
-
       self%sp_i => species(i)%obj
       self%sp_j => species(j)%obj