Added access check to student_proposal review.
Hosts and Developers can comment but not score an proposal (unless of course they are an org_admin/mentor).
Fixed the initial scoring being set to -4, which is annoying if you just want to comment.
Patch by: Lennard de Rijk
Reviewed by: to-be-reviewed
include COPYING
include mox_test.py
include mox_test_helper.py