Data Processor GUI improvements

• Rename "Data processing GUI" to "Data processing"
• The "Header" text is misleading because it only shows the "index" of the corresponding "Data Key", not all headers together with the selected "Processors"
  • Option1: Include the headers from the selected processors
  • Option2: Rename the field "header" to "index"
• The index/header information is not written to the scenario file, however, this information can be suitable for external software (such as the suq-controller). So this can also be written out to the scenario file, even though it never changes.