transferred OGSFileConverter-files from OGS5 to OGS6 and adjusted everything as needed
adjusted cmake files
fixed logog-problem and optimised code a little
added license information
replaced external call to file converter with instance of transferred dlg
removed file converter path from preferences dlg
moved file types enum to enum-class and added documentation
Merge pull request #493 from rinkk/FileConversionTool

File conversion tool