Merge branch 'feature/collisionPairs' into feature/electromagnetic

Merging branches and fixing a number of important issues:

- Initial particles were not being assigned to the list of particles.

- List of particles was being erased every iteration, even if species
  was not pushed.

These caused issues with the calculation of collisions when a species
was frozen.

Now, things should work properly. All particles are properly added to
the volume list and the list is erased ONLY if the species has been
updated.

I hope that collisions are now properly accounted for per species pair.

src/modules/moduleSpecies.f90

@@ -91,7 +91,7 @@ MODULE moduleSpecies
         part%species => self%ion
 
       ELSE
-        CALL criticalError('No ion defined for species' // self%name, 'ionizeNeutral')
+        CALL criticalError('No ion defined for species :' // self%name, 'ionizeNeutral')
 
       END IF
 
@@ -109,7 +109,7 @@ MODULE moduleSpecies
         part%species => self%ion
 
       ELSE
-        CALL criticalError('No ion defined for species' // self%name, 'ionizeCharged')
+        CALL criticalError('No ion defined for species :' // self%name, 'ionizeCharged')
 
       END IF