Issue61 dymola2015

This branch contains
- A change from protected to public for the parameter initialize_p in the energy balance. This was needed to avoid overspecified but consistent initial equations for finite difference heat exchanger models in which multiple volumes are connected in series. Otherwise, Dymola issues a long warning message.
- A change to examples to avoid overspecified but consistent initial equations.
- Some minor code cleanup.

The changes have been tested with the Annex60 and the Buildings library.