Remove metadata from Powerpoint Downloads

[mark-dce]

ACCEPTANCE Powerpoint downloads should be modified to contain:

• [ ] An initial slide with the collection title and description
• [ ] One slide for each image in the collection with the image taking up as much of the slide as possible
• [ ] No other content or metadata (i.e. remove the existing metadata slides)

PDF exports should remain unchanged: from the existing version

[mark-dce]

On reflection, this can be done but is probably out of scope since is really just a request for two export versions. We should discuss and respond prior to the demo. The SOW clearly indicates that there should be a version of the collection exportable to PDF or PowerPoint.

If we are going to do this, it should really be done completely by giving the user the option to export, then prompting them what file format (PowerPoint or Portable Document Forma), then asking which (if any) metadata fields should be included.

[mark-dce]

See #156 - determined that this it is out of scope to create a separate version of export for PPTX vs PDF.