Hide files and subtrees without any changes

[SwishSwushPow]

I think this has changed as part of the tailwind rewrite. Files and directories that don't include any changes are shown now, but I think they should be hidden again. I had my first look at the project today and just put together this small PR: #43

[xfbs]

I took #43 and expanded it slightly to add a button, now we can hide unchanged files + folders:

However, this currently is not the default (because it would break another workflow, which is to use diff.rs to view a crate's contents, which is used by cargo-vet).