Lessons Learned: add BibTeX edit UNDO functionality to Sniffer at least

[GerHobbelt]

It's much less stressful to run a set of documents, which already have BibTeX metadata attached, through the Qiqqa Sniffer (or other activities which intend to improve the metadata), when you can REVERT to a previous BibTeX copy for a given document when you note that the new stuff isn't what you expected.

This is not exactly editor undo/redo functionality you are used to in a generic text editor, but more like a "Woa! I didn't expect that to be such crap!" kind of Revert Now Panic Button.