ability to disable left or right swipe added.

Hey Ali, I'm creating a  custom container view controller using your awesome control. Basically the custom container view controller creates the entire Mailbox app view. That means it creates by default the UINavigationController, UISegmentedControl, and any behaviour and/or animation required to make it work.
I will share it through a new pod and it will have a dependency to your pod.

This pull request is just to prevent swipe to left/right when the first/last grid is selected.

Cheers!
martin