Add Instantaneous Email Notifications

Description

• Adds notification preferences to the profile page:

• Adds instantaneous email notifications when:
  • Application is submitted: (Subject: "Application (CSE1110) Successfully Submitted!")
  • Position is offered: (Subject: "Action Required: Position (CSE1110) Offered!")
    • Without Hiring Message:
    • With Hiring Message:
  • Application is rejected (also if offered/hired, then rejected): (Subject: "Application (CSE1110) Rejected")
    • Without Rejection Message:
    • With Rejection Message:
  • Declaration is rejected: (Subject: "Declaration (CSE1100) Rejected")
  • Declaration is approved: (Subject: "Declaration (CSE1100) Approved")

Related Issues

• Resolves #66 (closed)

Checklist

• I have added a changelog entry to reflect the significant changes I made.