Call styleContainer:animate:duration: in _handlePan:

When tapping the menu button, this method is called, but not when panning.

Some context:
While trying to mimic a sliding left menu (look at Spotify for iOS, for example) that moves a bit when panning the centerView I came across a solution that works fine when tapping, but not when panning. This commit adds the needed call to make use of the styleContainer:animate:duration method to make it work when panning too.