Hide left navbar tracks.

*The tracks fetch on the left nav will be a new feature that is not ready yet to go live. This was uploaded un commented by mistake.
Merge pull request #21 from mlopez-firstfactory/master

Level filter, fix question list when a new set is created
Add custom modal.

* this modal will be shown once the user gets into the final question of one set, to ask him :
- if he wants to continue working on the same track.
- or if he want to play in another track.
Improve styles practice page.
Modify Html directives in order to show answered percent even if the answers does not have any explanation.
Fix answers status and  missing method call.
Add hyphens when the user clicks on 'show answer'

Whenever the user clicks in the 'show answer option' we now display
hyphens instead of the actual data and as the wrong or right answer
icon.
Merge remote-tracking branch 'upstream/master'