SignUp class in views.py error fixed, membership class in teams' model error fixed

1. timezone.now() is not callable in DateField's default argument. So I applied to auto_now_add flag.
[ auto_now_add = Automatically set the field to now when the object is first created. ]
2. SignUp class in Views.py had been inherited by User in models. So It's removed.
3. Django 1.7 use built-in migration. I applied to it in buildbuild
http://soundatrumpet.tumblr.com/post/99427989846/migration-in-django-1-7-buildbuild