OriginalMetadata_FS_web_10349

See comments in https://github.com/openmicroscopy/openmicroscopy/pull/1026

This provides a "Download Original Metadata" button in webclient without referencing an original file (ID).
To test:
 - Import an image that generates Original Metadata (most do).
 - Also import some SPW data
 - Select an Image / Well, open the middle "Acquisition" Tab, expand the "Original Metadata" section and click the Download button.
 - Check the download Original_Metadata.txt. Should have lines of key=value pairs.