Add htmlentities to Exercice Title to avoid HTML issues

The title of an exercice is not made to have special design or html feature.
It is a title.
If the title of the exercice is
Example of <div> use
The text to display is this one, with html tags displayed as text
Merge branch '1.9.x' of github.com:chamilo/chamilo-lms into 1.9.x