sanitize markdown - #368

There are no tests. Just did :

• update mashlib with solid-panes@3.5.31-39483f75 and then

• npm run prepublishOnly

• npm run startStaticOS

• created a test.md resource with XSS issue using this sanitized example https://github.com/azu/safe-marked#usage

<script>alert(1)</script>
<iframe src="https://example.com"></iframe>

This is [XSS](javascript:alert(1))

• result is :

<p>This is <a>XSS</a></p>

I kept marked and dompurify separate for a better understanding if we ever decide to change one or the other package.