Assessment reports -> production branch

PR to production for issues #1594 and #1595


Copy of production branch with following 3 commits cherry-picked in:

f6de48a Assessment student data report (#1594)
c66e26e Addendum to #1594
9e5944a Assessment Summary report which replaces Problem set summary report (#1595)

PR for #1594 -> master has already been pulled. PR for #1595 -> master is outstanding.