Close #419 Radiation Adds HDF5 Output/Restart

This pull request:
- adds hdf5 via libspash to radiation plugin
- removes amplitude data as pure binary 
- instead adds amplitude data as HDF5
- adds correct checkpoints via HDF5
- adds automated restart
- improves seperation between communication and data write

It solves #419.

In upcomming pull requests:
- conversion factors to SI
- observer directions
- frequencies

will be stored in the HDF5 files as well
and tools for data analysis will be created. 
please explain the magic number