add excel export and PDF validation

We've added the ability to download an Excel export of the current Filter Tab view (including active filters) as a way of providing ad hoc reports to Vireo admins and reviewers. 

Also, we've implemented a PDF validator that currently checks for missing fonts in primary documents and prompts students to make the necessary modifications before re-uploading their document. This is a ProQuest requirement and could be of interest to any institution that would like to require a "minimally archival" PDF.