Delete addOnPageChangeListener method

[yital9]

Hi,

as I see, there are already a couple of questions, how to make your library work with the popular ViewPagerIndicator library.

Can you please just delete a ParallaxViewPager#addOnPageChangeListener(OnPageChangeListener listener) method, to make it possible to call the native method from ViewPager#addOnPageChangeListener(OnPageChangeListener listener)?
So it becomes possible to use not only 2 listeners.
Actually secondOnPageChangeListener field is unnecessary now, it can be removed too.

thanks in advance & best regards
Vitaly