RFE: do not reset expansion satus of folders in Unstaged files pane after commit

[ysalmon]

By default, folders are not expanded in the Unstaged files pane, which is nice.

However, it is not so nice that after having expanded some folders (and subfolders, etc.) and made a commit, everything is collapsed again.

Indeed, when one is breaking up a set of changes into multiple successive commits (so that each makes sense and can be more easily reverted or cherry-picked to another branch if needed), it is not rare that after having staged and committed files (or even part of files) in one or several deep subfolders, one will want to continue with the same subfolders for the next commit, provided there are still uncomitted changes in them.