Downloading all files only takes into account last digital object field

[MichaelRBond]

When downloading all files, the download only takes into account last file field that it finds.

1. $field_name should be an array of fields.
2. should create a directory for each field name to organize files before compressing
3. should provide a way to download ALL files or only for a specific field
   • On the files tab, if there is only one file form field, there should only be a "download" all option
   • add optional query string param "fieldName". If omitted, assume all file fields
     • if provided, omit the loop to determine field_names, just verify that we have a valid file field.
4. to facilitate this change, a directory structure will need to be created under the temp location
   • files should be symlinked into this directory (currently it just creates the zip archive from the originals)
5. If there is only one file (a vst majority of objects) there is no reason to display the Download all files link on the files tab. should be removed when there is only one file)