Set contact_sub_type for each registering student to 'Student'

We've added civicrm_contact.contact_sub_type column to allow us to use special templates when viewing and editing certain contact records (e.g. Students).

For the Quest implementation - we need this field set to 'Student' for each newly created contact record during Student "registration".

The logic to do this should be added to the quest.module - using civicrm_hook trigger. This can happen at the same time the new user's role is assigned.

(Paras - ping me if u need more explanation for this. dgg)