Volume: Add extra metadata options

[csparker247]

• DiskBasedObject: Add setMetadata/getMetadata member functions
• SkyscanMetadataIO: Parse the output directory name, which is usually a short-hand for the original reconstruction dataset
• Packager: If output directory is set in the input volume's metadata, save it to the Volume metadata under the original_dataset key. Temporary solution to keep track of where a volume came from.
• VC: Show the volume name alongside the ID in the volume selector
• Miscellaneous cleanup of docs and unnecessary void usage