add and use new creator property
continued work of !37 (closed)
KFileMetaData currently lacks the ability to extract information for file types that both have an author and creator tag. Also, a lot of metadata formats define a creator tag, which is currently mapped to KFileMetaData's author tag (though used in the same context).
This adds a new creator tag to KFileMetaData, then switches existing creator tag to use the new property, and finally adds extraction of the creator tag for the PopplerExtractor.