Disabling BugShaker breaks responder chain

[FabioTacke]

Hi!

When disabling the BugShaker the UIViewController still handles the shake gesture by doing nothing. That means that the responder chain is being terminated. I think it would be nicer to pass the motion event to the next responder (if any) in that case.

Consider the following example: I have an UIWindow handling a shake gesture. When enabling the BugShaker the shake gesture should trigger the alert asking the user to report a bug. However, when disabling the BugShaker I do not only want the alert to not being shown. I also want the UIWindow to handle the shake gesture instead.

If you like that idea I would love to create a PR.