Distinguish between creator, creatorTool and producer

[jstaerk]

We currently only support creator and producer and mustangproject puts creator in creatorTool which is probably wrong.

xmp:CreatorTool is set in xsb.setCreatorTool(creator) and means "The name of the first known tool used to create the
resource".
http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/xmp/pdfs/XMP%20SDK%20Release%20cc-2016-08/XMPSpecificationPart1.pdf
p. 27.

Creator respectively Producer refer according to
http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/pdf_reference_1-7.pdf
p. 844
to
Creator: (Optional) If the document was converted to PDF from another
format, the
name of the application (for example, Adobe FrameMaker®
) that created the
original document from which it was converted.

respectively
Producer: (Optional) If the document was converted to PDF from another
format, the
name of the application (for example, Acrobat Distiller) that converted
it to
PDF.