GTreeView: Support multiple root-level items

Previously it was only possible to have a single root-level item in a
GTreeView. This was an oversight and I didn't realize it because this
code was only ever used in the FileManager, which has one root ("/").

Also factored out item toggling into a separate function, and increase
the base indentation level so that root items can be toggled as well.

Finally, let the user toggle the selected item with the spacebar. :^)

0 files changed, 0 insertions, 0 deletions