Increase performance in shell scripts

[matzegoebel]

There are several points where performance in the shell scripts (first CMOR step) can be optimized:

• Include option to concatenate variables to yearly files directly from the one-timestep files (no intermediate monthly files).
  To allow using the CCLM Starter package (which produces monthly time series) it should, however, remain possible to work with monthly files in the second part of the shell scripts (second.sh)
• Write a python script that is executed from master_post.sh and that calls the shell scripts first.sh and second.sh. In this python script the processing of different years can be parallelized (with multiprocessing, similar as in the cmorlight.py python script)