#2029 - New relation examscore -> examrecordscore

**Note: Migration required for this change.

I'm setting this new relation in 2 instances:

1. Autograded responses. For this the examrecordscore related to is the
one corresponding to the score with penalties excluded.

2. CSV grading. For this, the examrecordscore related to is the one
which is for the latest submission (attempt) at the time of csv upload.
This is because csv grading, as currently works, posts grades to the
last submission for that exam. In this instance, the score on the
examrecirdscore is the same as the examscore as there are no
machine penalties applied with csv grading.

What I have not touched is the regrader. The reason being, that I'm only
setting relations for new submissions, not retroactively. It ought to be
easier to incorporate after current courses have died.
The case where csv grades are being set for a student who has not
attempted this exam yet needs to be handled.
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
#2298 Added "Username" as column title for Student Scores in-line
report
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Someone stole my migration placeholder.
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Getting last examrecord with max(score).
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
Start of relation populate new method.
Hides publishing model for videos and assessments from instructor #2319
Merge branch 'master' of github.com:Stanford-Online/class2go into kluo-2319-hide-draft-mode
Commiting and pushing this to see if it is Travis friendly.
Merge branch 'master' of http://github.com/Stanford-Online/class2go into dca_new_working2
#2029 - Hopefully the last commit.

Includes:
Migration 008 that creates the relation field
Migration 009 that back populates the relation
Code to set the relation on csv upload for csv graded type exams
Code to set the relation for all other types of exams on submission