fixed Unit.get_unanswered_uls() to only list core sequence questions
fixed Unit.get_unanswered_uls() to only list core sequence questions

raccoongang/socraticqs2,cjlee112/socraticqs2,derdmitry/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2,raccoongang/socraticqs2,derdmitry/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,derdmitry/socraticqs2,raccoongang/socraticqs2