Add Markdown Viewer

Description / Overview

We currently only handle the rendering of AsciiMath in our correction overview. Since students will always write more Markdown than AsciiMath, we'd like to have some way to render the Markdown. Ideally, we'd like to have a dedicated dialog that just displays the fully rendere Markdown, including AsciiMath. This dedicated dialog could be implemented in the same manner as we currently render the Jupyter notebooks.

In another breath, we can discuss if we want to keep the AsciiMath renderer that's directly incorporated into the correction overview, as it turned out to be unreliable and error prone in the past.