Add new notification email.

openedx/core/djangoapps/ace_common/template_context.py

...edx/core/djangoapps/user_api/accounts/tests/test_views.py

openedx/core/djangoapps/user_api/accounts/views.py

openedx/core/djangoapps/user_api/message_types.py

...r_api/edx_ace/deletionnotificationmessage/email/body.html

...er_api/edx_ace/deletionnotificationmessage/email/body.txt

...i/edx_ace/deletionnotificationmessage/email/from_name.txt

...r_api/edx_ace/deletionnotificationmessage/email/head.html

...api/edx_ace/deletionnotificationmessage/email/subject.txt