Update pagination.js

it makes more flexible customization of pagination. for example i can put pagination to any place (via html), and i can put to pagination other elements.

like
       ...
        <div class="slides-container">
            <img src="images/slide1.jpg" alt="">
            <img src="images/slide2.jpg" alt="">
            <img src="images/slide3.jpg" alt="">
        </div>        
        <nav class="slides-pagination">
            <div class="slides-navigation">
                <a href="#" class="next arrow right" title="Next"></a>
                <a href="#" class="prev arrow left" title="Previous"></a>
            </div>
        </nav>
       ...