Hide comments in visual mode

[0nko]

Add a configuration option to hide the HTML comments in visual mode (in preparation for Gutenberg).

[maxme]

There might be another change to consider to support basic Gutenberg blocks: images are wrapped in a figure tag like:

<!-- wp:core/image {"id":316} -->
<figure class="wp-block-image"><img src="https://bia.is/hola-que-tal.jpg" alt="" /></figure>
<!-- /wp:core/image -->

Aztec could simply ignore visually these tags as a first step.

[daniloercoli]

Fixed in #592