Add missing Grade object for student dashboard.

Closes #301.
See #312.
Fix errors with grade creation and association.

See #203.
Work on creating self-logged grade objects.
Self-logged grades working.

Closes #203.
Fix argument error.

CLoses #312.
Only allow submissions when assignment is open.
Redirect if assignment is no longer open.
Merge pull request #314 from bellotastudios/self-logging

[Reviewed] Self logging of grades.