Instructors should get email notifications for pending requests

[cycomachead]

We should have a new course setting:

"Send [Dropdown] notifications of all pending requests to [email field]"

The dropdown should default to nil / no
Other options should be "daily", "once weekly" .
Weekly can default to Fridays at 5pm

Later we can add "2x weekly"
Tu/Th
and "3x weekly"
M/W/F

depending on how easy it is to setup.