Implement frontend for Payment service

[momciloknezevic7]

1. Right side for student role (student debts)
2. Left side for student role (payment slip with five fields and pay button)
3. Left side for administrator role (payment slip with three fields and pay button)
4. Right side for administrator role (field for username and delete button)

• Also, enabled CORS and update return values for some methods in controller

[momciloknezevic7]

Closes #132