Add a handlebars helper for Experimental section

[rpowis]

Please add a handlebars helper for Experimental: section, to

• remove the Experimental: text OR
• make 'Experimental' a bold heading element

[rpowis]

We can't remove the Experimental: text because otherwise how would it know it's experimental.

We should be able to automatically bold the text and separate the description though...

/*
Modal Dialog

An accessibility compliant & responsive modal dialog box module.

Experimental: Before considering this design pattern, make sure that you have strong evidence that:
* There is a real user need to have attention focused on a single piece of content;
* That need cannot be met by taking the user to a new page in the same flow that contains the crucial piece of content;

<button href="#" class="button" role="button" data-modaldialog-action="open" data-modaldialog-target="example-modal" tabindex="1">Open example</button>

Markup:
<div class="modal-dialog modal-dialog--hidden">
</div>

Style guide: Modal Dialog
*/