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
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html