Drupal catalogue-modules: CSV-import/export

Related to mbexc#30.
The CSV-importer/exporter has been developed as agreed on in the Werkvertrag. The module allows for the import/export of Drupal Content (such as it is used in the FlyStock Module) via .csv file for example.
A demonstration by Peter Kiraly introduced the state of development.
The functionality needs to be installed and tested on the dev-mbexc instance.