Added setter for a submission's rubric_assessments
Pagination support for assignments and freeform rubric comments

 - Added nextPage method for assignmentslist
 - Added ability to grade a submission using a rubric assessment
 - Added support for freeform rubric comments for assignments
Merge remote-tracking branch 'upstream/master'
Fixed spelling on assessments
Merge pull request #67 from hhoang/master

Added setter for a submission's rubric_assessments