fix netCDF compression

due to the bug describe in #78 (closed) concerning the compression with nccopy, a solution needs to be implemented which is able to do error handling or simply deal with faulty (uncompressed) netCDFs.

First option

• Investigate python native solutions to compress NetCDFs
• if no python native solution is found, implement the subprocess call to nccopy that detects errors, and in the event of an error, scraps the compressed file.

/cc @mschleiss