The ability to navigate back and forward the function selections #54

The drill down for the function to its children is really nice.
But sometimes, a function has multiple parents, so it's not always obvious which one to go back to.
It would be great to be able to go back to the previous function with a Back button (and vice-versa forward with a Forward button). This would behave like a browser. Having it work with the mouse "side-buttons" that are often mapped to back/forward would be great also.