CK5 panel plugin blows away h5 elements

@joseph, thanks for creating this ticket! It's nice to have the large sites at AAFC with legacy CKE4 data to catch all of these issues.

Here is the specific markup in question:

<section class="panel panel-default">
    <header class="panel-heading">
        <h5 class="panel-title">
            Panel title
        </h5>
    </header>
    <div class="panel-body">
        <p>
            Panel body.......
        </p>
    </div>
</section>

The issue is, the wxt_panel plugin has the heading level hardcoded to h3.

I already made the heading level configurable with the wxt_alerts plugin for a similar issue, and WCAG (setting proper heading levels). I will make the same changes to the wxt_panel plugin, to allow any heading level from h2 to h6.

@joseph this has been fixed and merged with 6.1.x. Now we can support any heading level from h2-h6 within the panels without markup being stripped.

Perfect, thank you for the very quick response and fix!