Adds controls in the itemgroupeditor to simulate the itemgroup that is being configured. I copied the algorithm from the container.gd script, so if any change is made to either, the results will be off unless every instance of the algorithm is changed.
Requires #408 Fixes #405 Fixes #406
This PR does two things:
container.gdscript, so if any change is made to either, the results will be off unless every instance of the algorithm is changed.