:recycle: Refactor image readers with more shared logic

[aaronleopold]

Resolves #210 Fixes #283

• Unify some of the rendering and logic for the image-based readers, allowing for more seamless transitions between paged vs continuous reader(s)
• Updated some VERY old OPDS code which caused a bug using Yomu
  • Side note: I would like to do a rough pass through all of the OPDS logic before 0.1.0, as it is generally the oldest code in the repo
• Added local preferences for adjusting preload options in the image readers. If people would rather this be persisted to the DB I can adjust it
• Adjusted a few misc styles