Todo;
include display support for .pdf
Add New Document:
Create new ss in img folder
Change name of ss to its sheetId
Make sheetId part of Doc entry
Edit Doc
If Front or Back changes
Chunk, Enc and update SS:
Row 1 for Front
Row 2 for Back
Can't support arbitrary nbr of images per doc because ss will fail at ~> 15Mb
Delete Doc
Remove corresponding img file