first half of #71 implemented (needs to be fixed also for list exporter)
fixed copyright for mimefileexporter
fixed copyright for list exporter
fixed #71
implemented Open Folder View for List-Exporter and Exporter node (fixed #73)
renamed output files node from ListMimeFileExporterNode to OutputFilesNode
renamed output file node from MimeFileExporterNode to OutputFileNode
Merge branch 'feature/open-output-folder' into develop