Config validation

Add field checks for configuration file. Uses tests/input_files/config.yaml as template and compares current config fields to this one.

The tests/input_files/config.yaml is extended to use the field optional to mark certain fields as optional (i.e. can be deleted). This requires a new md5 sum in tests/test_scripts_prepare_inputs_table/expected_output.md5.

Also adds the possibility to add optional author information into the multiqc report.

Closes #78 (closed) and #174 (closed)