Icon generator window refactor
Can now be run from anywhere, regardless of scene
Runs a realtime viewport with moue controls for zooming, panning and rotating
Added a button to match another prop renderer, copies all of the settings from one prop renderer to another
Added an overlay option, loads a sprite and overlays it on the viewport with a fade slider so we can eyeball match icons
Open icon generator button int he inspector now opens the window, doesn't change scene
Fixed prefabs that have a PropRenderer but were not found in the icon generator list - any PropRenderer in the project will now appear in the list after a refresh (refresh takes twice as long though)