Add ability to refresh and re-sort "Folders" panel

[marp]

Currently (1.8.2), there seems to be no refresh capability of the "Folders" panel.

While the "Folders" panel automatically detects new folders, folder deletions and folder renames, it does not seem to be able to sort new or renamed folders.
Instead, such folders are added at the bottom of any given folder sibling hierarchy.

The only way to get properly sorted folders in this panel is to entirely quit the application and restart.

Best Regards,
Marp.