Student search: Not respecting look ahead and look behind

[marcusboon]

These overview dashboards are very useful while the exams are in progress, but exams usually run over time for whatever reason (students with special considerations, file uploads, etc). So the ability to configure to show recently completed exams (say closed like an hour or two hours ago) would be immensely helpful.

[mattporritt]

There looks to be two issues here for the student search functionality:

• Look ahead and look behind functionality isn't working, correctly. Look behind should pickup quizzes that finished in the last x hours. Look ahead should find quizzes starting in the next x hours.
• Student overrides are not being taken into account in the calulations

[mattporritt]

@guillogo When we merge the branch for this issue in, we'll also have to cherry pick it into the other branches

[mattporritt]

@guillogo I think this update may have broken the heatmap on the assessment dashboard. It looks like all days have the same "heat" and the scale looks messed up.