Student with no powers crash fixed

views.py -> if statement included to check if the student has powers or
not, if not, assigns him/her all powers to zero.

models.py -> "unlock_nickname" bug fixed - there was an extra "s" at the
end of the name (unlock_nicknames).
Power names updated to Qubal v0.3 version:
social_skill -> teamwork
activity -> perseverance
index.html -> vars with all power names updated with new ones, in html
tags and javascripts