Refs #389: Updates course objectives to have start / finish dates and active field. Active field addition required some fairly broad updates due to queries all through the application. Also fixes bug in curriculum explorer where events with mapped objectives and without an audience weren't being counted.
Brings feature-course-objective-dates in line with develop so as to merge branches cleanly.
Merge pull request #422 from EntradaProject/feature-course-objective-dates

Refs #389: Updates course objectives to have start / finish dates