Area vector closure check

[mbarone81]

Within the code, integrate control volume face area vectors to check that the integral is zero for each volume.

[spdomin]

The poor man's check is to activate a heat conduction case with all dirichlet and ICs of the same constant value. Then, output the projected nodal gradient, e.g., dtdx to verify that it is zero.

Otherwise, would be far more user friendly for the code to do this.