Add the ability to delete a property from the property editor

[kenzieschmoll]

Once you set a property, there is not currently a way to unset the property other than by manually deleting the property in the code editor. It would be nice to have a way to unset or delete a property from the property editor. Here's an idea of how we could to this in a way that takes up minimal space.

CC @mit-mit, who originally gave this feedback for wanting a way to delete a property without being forced to go back to the code editor.