Add script to run identify-main-identifier on folder, add Wiener Library pre-processing

The Wiener Library files needed an EHRI main `<unitid>`. To add it to all files, I created the shell script that calls the *identify `<unitid>` as main identifier* pre-processing on a complete folder.

I noticed that many `<persname>`, `<corpname>`, `<geogname>` and `<subject>` contained `<emph>` elements containing the data in parts. This broke the importer (even with `wienerlib.properties`), so I added a pre-processing step (in XSLT :)) that joins the text values by `, ` and a script that runs the conversion on all files. Finally, the XSLT also removes (the one) empty `<subject>` element(s) - although such empty elements should probably be ignored during import.