Improved DiffList

The DiffList now uses a ChangeListEntry struct instead of single variables in the callback. not sure about the `QVector<ChangeListEntry> DiffList::changes()` method. I'll try that out in one of the next commits.

Going further: Thinking about the PatchConsumer, it uses the same variables in the startFile() callback. It could use the same struct here, right? If so, I would like to change it in this PR.

Btw.: There was a little bug in the changeListCallBack() method a wrong handled bool. That caused only the first change to be noticed and returned an error after that -> Fixed it.