Breaking model

Apply text provided by @mtbc regarding breaking changes to the 5.0 model: namely `OriginalFile.sha1` --> `OriginalFile.hash`. Since there was no clear landing page for putting the breaking info, I put some under `whatsnew` and the details with the matching documentation.
Noted, but unfortunately this isn't (yet) a config property. I debated saying as much in the text, but thought that would be confusing. Thoughts?