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. 
Is this part of our code style?
It shoudn't: see (https://blog.codecentric.de/en/2014/02/curly-braces/?utm_source=dlvr.it&utm_medium=tumblr)[Apple's curly braces bug]