Find a canonical way to block input to the whole screen and/or make blocking modals

[WildWeazel]

PopupOverlay.setMouseFilter recurses through the scene to update the mouse filter on every Control node. Investigate recommendations for how to accomplish this, and make it a generic function that can be used anywhere.

Original comment:
let's make a TODO to look for a pattern for this. there has to be a better way than recursing through the whole scene

Originally posted by @WildWeazel in #409 (comment)