Support multiple top level DOM elements for a component

[mlrawlings]

In a way, this is the relates to/is the inverse of #392 which would allow an element to be bound to multiple components, and removes the need for a wrapper element.

Right now there is the limitation that a component can only be bound to a single element.

If I have the following:

<h1>The current count is, ${data.count}</h1>
<button>Increment Count</button>

And want to bind a component, I will have to wrap them with another element:

<div w-bind>
    <h1>The current count is, ${data.count}</h1>
    <button onClick('incrementCount')>Increment Count</button>
</div>

It's also a little weird that you can have markup for a widget that isn't bound to the widget:

<div w-bind>Hey, ${data.name</div>
<div>I'm just here, not actually bound</div>

If, instead we could bind all top level DOM elements in a template that is set to be a component, that would mean no need for w-bind (assuming we use the presence of a component.js or widget.js to indicate that this should be a component).

It would be nice if the following just worked:

<h1>The current count is, ${data.count}</h1>
<button onClick('incrementCount')>Increment Count</button>