Channel manager: container&container-item elements are restricted to one className

The elements that are denoted as either container or container-items can only contain a single className; hst-container or hst-container-item. This makes it hard to use frameworks like Bootstrap.

The following is currently not possible:

<div class="row-fluid hst-container">
<div class="hst-container-item span4">Text here</div>
<div class="hst-container-item span8">More here</div>
</div>