Merge pull request #864 from edx/adam/welcome-email

lms/djangoapps/instructor/tests/test_legacy_enrollment.py

lms/djangoapps/instructor/views/legacy.py

lms/templates/emails/activation_email.txt

lms/templates/emails/activation_email_subject.txt

lms/templates/emails/enroll_email_allowedmessage.txt

lms/templates/emails/enroll_email_allowedsubject.txt

lms/templates/emails/enroll_email_enrolledmessage.txt

lms/templates/emails/enroll_email_enrolledsubject.txt

lms/templates/emails/unenroll_email_allowedmessage.txt

lms/templates/emails/unenroll_email_enrolledmessage.txt

lms/templates/emails/unenroll_email_subject.txt