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/init/moduleInput.f90

@@ -637,7 +637,6 @@ MODULE moduleInput
       CHARACTER(:), ALLOCATABLE:: electron
       INTEGER:: e
       CLASS(meshCell), POINTER:: cell
-      INTEGER:: subSteps
 
       !Firstly, check if the object 'interactions' exists
       CALL config%info('interactions', found)
@@ -771,13 +770,8 @@ MODULE moduleInput
               pt_i = speciesName2Index(species_i)
               CALL config%get(object // '.species_j', species_j, found)
               pt_j = speciesName2Index(species_j)
-              CALL config%get(object // '.subSteps', subSteps, found)
-              IF (.NOT. found) THEN
-                subSteps = 1
 
-              END IF
-
-              CALL coulombMatrix(i)%init(pt_i, pt_j, subSteps)
+              CALL coulombMatrix(i)%init(pt_i, pt_j)
 
             END DO