(WIP) Mentoring assessment mode

The work of assessment mode. 

Currently missing:

* Taking into account the max_attempts
* Make all light children have their own *weight* for score
* Test in client app 

CC @antoviaque if you want to review and give it a try in the LMS
This could be a simple wrapper around the `render_template` function that simply adds the `<script>` part around what the other function renders.