Multi Species Particle Load from hdf5

- rewrite how partilces are loaded from HDF5 file
- add support for arbitrary species count
- particles load now done on gpu
- remove old method
- SimulationHelper: show init time in output

**Please do not merge before #514**
I don't like that we have so many log messages here for every detail of the loading process (e.g. `mapped memory`, `get device ptr`, ...). Please only include log messages that are really necessary. Otherwise, during a normal load, the log grows very large without much additional information.