Store attributes on the file root instead of table

Storing attributes on the file root speeds up the read out.
Now you do not need to get the groundparticles node first.
Problem described in a comment in #18

Show no progressbar when there are only one or no particles.
Since progressbar does not like a maxval of 0.
Add cleanup to qsub_store_corsika_data

Remove script after submitting to Stoomboot.