WD: better support for "all-files-in-folder" processing

Improve whole folders processing by WD readers

1) Allow to select folders from GUI

2) Add options: 'recursive' and 'file-handling-mode' where 'recursive' will force WD to process folder recursively and 'file-handling-mode' will tell if to filter files with no data / bad format or generate default empty values for all of them.