Add toPage argument to .goBack()

Issue #406 seems to have gone nowhere because the contributor didn't fill out a CLA.

I've just filled out a CLA 5 minutes ago (although curiously it had the wrong IP, is it using a load balancer IP instead?). Happy to fill out anything else if needed.

Attached is a new patch to solve the same issue, written without reference to the original code [although based on line counts theirs seems to be significantly larger -- I just rewrote the history before calling doNavigation() -- did I miss something else I needed to do?]