Closed Issue: Microdata in Visual Editor [2128]

When working with Microdata (https://schema.org/docs/gs.html) in the Visual Editor (source mode), many of the important tags are stripped when you want to save the page.

Ie. the following

```
<div itemscope="itemscope" itemtype="http://schema.org/EmailMessage">
<div itemprop="potentialAction" itemscope="itemscope" itemtype="http://schema.org/ViewAction">
<link itemprop="target" href="https://watch-movies.com/watch?movieId=abc123"/>
<meta itemprop="name" content="Watch movie"/>
</div>
<meta itemprop="description" content="Watch the 'Avengers' movie online"/>
</div>
```

is stripped to

```
<div itemscope="itemscope" itemtype="http://schema.org/EmailMessage">
<div itemprop="potentialAction" itemscope="itemscope" itemtype="http://schema.org/ViewAction" />
</div>
```
Comments: Fiedx, more on https://github.com/Orckestra/C1-CMS/issues/15