Fix useless READ MORE markdown

In some cases, the "Read more button" is clearly useless (eg: https://rex.dri.utc.fr/app/university/203/previous-exchanges).

Before button click:

After button click:

We need a better heuristic on when to hide the button (and show the whole text) and when to do the opposite.

Edited Apr 04, 2020 by Florent Chehab

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