Move PhotoDemon name + version code to standalone function

So it can be used in multiple places
Improved treatment of technical JPEG metadata

Some technical JPEG data (YCbCr positioning, etc) can be stored in the
file's EXIF or XMP sections.  When re-saving a JPEG, such data may have
changed - so instead of blindly preserving it, rewrite it to match the
current technical data.

Also, when in non-privacy mode, PD is now listed as the last edit
software.  When in privacy mode, all software data is removed from the
file, and I have added code to prevent ExifTool from automatically
noting itself as the XMP Toolkit if XMP data is present.