Fix #3347: "Run Code" reloads page in Matlab Problem

Instead of refreshing only the necessary parts,
"Run Code" reloads the whole page.

This commit fixes this behaviour, by refreshing the
specific elements belonging to the Problem instead.

Internal number:  LMS-2505

@antoviaque and @dianakhuang might be interested.
@adampalay @waheedahmed We get the response, and essentially replace just part of the problem. (fade-in is just a visual cue, so that the user takes note of it.)

The alternative was refreshing the whole page, which was highly disruptive.