Support for renaming files

[koppor]

I tried gumtree on a "random" Pull Request. There, I renamed files. The output is as follows:

While GitHub also thinks only one file is renamed (scroll down at https://github.com/JabRef/jabref/pull/10847/files), I would like to be able to drag and drop rennamed files to give GumTree a hint which files to compare.

(Follow-up to #329)

[jrfaller]

That would indeed be nice to have! Renaming detection is far from being a bulletproof feature. However, I think it would require a significant rework of the list view so I am marking this help wanted for now