Slideout menu won't work if html contains words 'slideout-menu'

[ingria]

This doesn't work:

<!-- I'm binding my js to bem-like markup with js- prefix, not IDs: -->
<nav class="js-slideout-menu">
    ...
</nav>

Because this will return true.

Script's logic should be similar to element.classList.contains() method.

[pazguille]

#196