I would like to integrate this content as iframe or Onebox:
https://snap.berkeley.edu/project?user=bh&project=py-fractal
What needs to be done to achieve that?
Add https://snap.berkeley.edu/ in the allowed iframe site setting and then you will be able to embed the URL into an iframe on posts:
<iframe src="https://snap.berkeley.edu/project?user=bh&project=py-fractal"></iframe>
You should also set width and height and other parameters
<iframe src="https://snap.berkeley.edu/project?user=bh&project=py-fractal" width="xxx" height="xxx"></iframe>
How could I just overlook the iframe option in the settings? Thank You 
In your admin panel search for “iframe”.
Here <iframe>: The Inline Frame element - HTML: Hypertext Markup Language | MDN a quick guide to the attributes you can use inside the iframe tag on post
Sorry, i found it before. I asked myself how i could have overlooked.
It’s surprising just how useful the search feature of the site settings is. I almost never interact with system settings any other way. Even though you’d figured out it, it bears repeating for others with similar problems.