Fix nopathtoitem error in peer grading
Address review comments
Fix problem with peer grading list not rendering, test
Address review comments
Fix linking problem for peer grading, add in a test

Conflicts:
	common/lib/xmodule/xmodule/tests/test_peer_grading.py
Merge pull request #971 from edx/fix/vik/pg-hotfix

Fix/vik/pg hotfix