Move creating/updating wdbmeta to file update trigger?

currently, meta data entries in wdbmeta are created/updated by `rest2/rest-common.xqm`

This will have to be invoked from all functions creating/updating files; hence, it does not work when manually uploading/updating files (which might just be necessary from time to time).

As we are already using the file update trigger, it might be easier to simply move meta data handling there.