PDF export

Copy-pasting @nickstiffler's description from !181 (closed) here.

@yannis We couldn't wait on this any longer as we receive frequent requests for the PDF view. Let me know if you have any suggestions on how this should be implemented or if this is ok for now. My plan it to export to PDF directly from the app using Puppeteer https://developers.google.com/web/tools/puppeteer, so this will be temporary.