Email confirmation enabled for teachers

Enabled devise 'confirmable' feature to turn on email confirmations for accounts.
Some custom logic for our service:
(1) All accounts will continue to work without confirmation & student accounts will still not require an email address
(2) New teacher accounts will receive an email to confirm their email address during account creation
(3) Students that become teachers later are now required to have an email address and will be asked to confirm their email address
(4) Teacher prizes will require a confirmed email address