Change gantt component-finding to use classname.

I put a page on my server to load with the `template-url` attribute of the `gantt` directive. I wanted some custom styles to be used by all my stuff, so I did this:

    <div class="gantt">
        <style type="text/css">
            /* my styles */
        </style>
        <div class="gantt-labels" ... >
            ...
        </div>
        <div class="gantt-head" ... >
            ...
        </div>
        <div class="gantt-scrollable" ... >
            ...
        </div>
    </div>

Some stuff in my gantt broke when I did this, such as the `onScroll` event. I checked it out, and it appears that it finds the `gantt-scrollable` element by just counting children. Adding my `style` element made the count wrong, and the grid broke.

What's your opinion about using the `$element.find` instance method for this?