[Enhancement] Closable top-level folders

[benjamw]

The problem

When viewing the contents of Cryptr, my sidebar has quite a few top-level folders (the "SECRETS" value in the image in the README).
Those top-level folders also have quite a few entries in them, requiring me to scroll very far to get to the content I'm looking for.
It would be nice to be able to click and open/close those top-level folders to shrink the space used in the sidebar, much like how the inner folders can be opened/closed on click.