Refactor folder navigation to use css keybindings

[Bios-Marcel]

Taken from GIMPNet IRC:

<marcel> Heyho, can anybody tell me how to prevent a widget from consuming a specific key event? I have a TreeView and it consumes the events of the keys "Left" and "Right".
<albfan[m]> marcel: you need to override keyevent managing and return false on those keys
<marcel> How'd I do that? I was looking the documentation for Gtk.Widget and couldn't find anything like thta.
<al> marcel: i think https://valadoc.org/gtk+-3.0/Gtk.Widget.event.html is worth a try
<marcel> I see, thanks, I shall take a look at that.
<al> and https://valadoc.org/gtk+-3.0/Gtk.Widget.key_press_event.html
<marcel> Well that's the event, I can't override anything in the event itself, right?
<marcel> I thought a signal doesn't have any logic, it's basically just a connector
<al> in you class you want something like: public override signal bool key_press_event (EventKey event) { return false; }
<al> if that works for all keys then write some more code just to file left and right
<al> *filter
<al> oh and drop the signal, public override bool key_press_event (EventKey event) { return false; }
<al> i'm probably getting confused, you want key_press_event.connect, but have a look at https://wiki.gnome.org/Projects/Vala/SignalsAndCallbacks