Draft: Updates for DFTB+ calculator achieved during ASE/Fireworks workshop

Not sure if it can safely be merged. Passes the DFTB+ tests, but there are just a few of them. The main thing we did is updating the code to the DFTBProfile and DFTBTemplate structure. Some of the methods of the old DFTB calculator class are not (yet) available in this new code structure though. Some feedback on it from your side would be great to continue working on the calculator update.