Items in Cabinets

Part of this game is going to be searching through the house for items, and as such some items will be contained within cabinets. I’ve added code to Openable to handle this; now, one item can be contained within an Openable, and will be revealed when it’s opened.

Unfortunately, Godot doesn’t handle propagation of click events in overlapping Area2D instances like it does other events; it looks like unless I write some code to handle that myself, I’ll need to make sure that Openables that have items in them don’t have a description of their own. I think that’s probably okay.