Fix for Issue #174 - pageAppeared Delegate Callback

[JakeSc]

#174

There is a bug in which tapping a page to advance does not call the delegate callback pageAppeared. This is because the tap IBAction sets the new _currentPageIndex before the notifyDelegateWithPreviousPage gets called. This latter method has a check which fails when the currentPageIndex is updated before calling it.

This PR resolves this bug by just making the tap IBAction scroll to the page index and not update the currentPageIndex. Then in the scrollDidEnd callback, we update new currentPageIndex already.

Note that in #174 , this bug still exists when one calls the setCurrentPageIndex: method. My recommendation is to not expose the setCurrentPageIndex: setter, and instead expose the scrollToPageForIndex: method. Then, we only ever update the new currentPageIndex property once, after the scrollView delegate callback is called.

[JakeSc]

I exposed the new scrollToPageForIndex: method in the header file. Calling this is essentially the same as calling setCurrentPageIndex:animated:, except for the fact that it doesn't actually set the _currentPageIndex. This happens after the scroll has occurred.

[JakeSc]

I did this so that I can add an NSTimer that automatically advances pages, but still have that pageAppeared delegate method called.

[ealeksandrov]

Thanks a lot for your contributions, looks awesome!