allow nested childrens for slideSelector

[gajdy]

This commit allows to set slideSelector as nested children of bx container. I'm using .page as slideSelector for big resolutions and .slide for smaller

<section class="bx-wrapper">
<div class="page">
<div class="slide">content</div>
<div class="slide">content</div>
<div class="slide">content</div>
</div>
<div class="page">
<div class="slide">content</div>
<div class="slide">content</div>
<div class="slide">content</div>
</div>
</section>

[RyanONeill1970]

Would agree this is a very useful patch, the older versions of bxSlider used to do this and upgrading broke due to our sliders using sub elements.

[machwatt]

Any updates on that? Since children() only traverse a single DOM level, this could be very helpful.
Or is there another way to implement the behaviour as described above?