In app jpg and pdf support

Hi jimger:

There are complications regarding expectations about what happens to previewed files when the app locks, as well as the possibility of data loss if one believes the files can be edited on disk. To simplify the situation, we settled on the "Download" behavior you see now. We felt that at least for this initial implementation, making it clear what data is decrypted by having it be visible in the Downloads folder, was a sensible choice. We're always investigating ways we can improve based on feedback from users like yourself.

I've added your feedback to our internal discussion on the subject. Thank you for your input!

Jack

ref: dev/core/core#8252