Add dynamical allocation of levels to the SE dycore

[nusbaume]

Currently the number of vertical levels is set using a pre-processor definition, and thus can't be modified after the model is built. It would be better to instead have the number of vertical levels set at run-time, but doing so requires having the SE dycore dynamically allocate certain variables during model start-up.

The code to do this allocation has already been written for CAMDEN, but it would be beneficial to bring it back into CAM. That way any future developments will be easy to port between the two models.

Finally, this modification will not be made until issue #392 has been fully taken care of and closed.

FYI: @PeterHjortLauritzen @jtruesdal @gold2718