Basic PDF support

[aaronleopold]

The server needs to be able to: process, properly handle and serve PDF files. This issue is for basic support, page streaming support will either roll out separately or, depending on how the rest of the below goes, at the same time.

Core Tasks:

• [ ] Add logic to detect PDF mime
• [ ] Add logic for PDF operations:
  • [ ] Simple file serving
  • [ ] Thumbnail extraction and/or generation
  • [ ] Metadata extraction / interpretation
• [ ] Start accepting PDF files during scan

Interface Tasks:

• [ ] Epub Reader