How to add a new collision operator:

Create a class that inherits from CollisionBase and include the method doCollisions that does the
operation. The constructor should call the CollisionBase constructor with the collision
name argument and read in any input parameters with a prefix of the collision name that are
specific to the operator.

If the collision is a binary collision, the new class may be a version of the templated
BinaryCollision class. The specific collision physics is in this case defined in a new functor,
acting at the cell level, whose type is the template parameter of the BinaryCollision class. See
for instance BinaryCollision<PairWiseCoulombCollisionFunc> for an example.

Then modify CollisionHandler.cpp to include the header file of the new class. In its constructor,
add an if block for the input collision type creating an instance of the new class in the
allcollisions vector.