Fix save button functionality

[mayhewsw]

Currently, it works like this: if there are no changes to a document, then you can't save it, and it marks it as "saved" even though it's not actually stored in the annotations directory.

There should be 3 states:

1. in the annotated directory, unchanged (should say "saved :)")
2. not in the annotated directory, unchanged (should say "save")
3. changed (should say "save")

One complication here is that the code will automatically save documents when you look at them. If you look at a document, make no changes, and click through to the next one, that will save the doc, even though you didn't intend it to. I'm not sure what to do about this!