title: Multiple Slick Sliders Issue
body: <p>I am using Slick.js plugin with its Slider Syncing feature. The issue I am having is that if I use multiple sliders on a single page, by clicking next or prev buttons plugin performs the action for all sliders on page. I wonder is there anything I could do with JQuery to have the next and prev work for each slider on page not for all? Thanks in advance. </p>
  
  <p>HTML</p>
  
  <pre><code>&lt;div class="slider"&gt;
      &lt;div&gt;Item 1&lt;/div&gt;
      &lt;div&gt;Item 2&lt;/div&gt;
      &lt;div&gt;Item 3&lt;/div&gt;
  &lt;/div&gt;                                                            
  &lt;div class="slider-nav"&gt;                                  
      &lt;div&gt;Item 1&lt;/div&gt;
      &lt;div&gt;Item 2&lt;/div&gt;
      &lt;div&gt;Item 3&lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>SLICK RUN SCRIPT</p>
  
  <pre><code>$('.slider').slick({
      slidesToShow: 1,
      slidesToScroll: 1,
      arrows: false,
      fade: true,
      asNavFor: '.slider-nav'
  });
  $('.slider-nav').slick({
      slidesToShow: 4,
      slidesToScroll: 1,
      asNavFor: '.slider',
      dots: true,
      arrows: true,
      centerMode: false,
      focusOnSelect: true
  });
  </code></pre>