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.
Refs #351: Adds ability to sync course group members via ldap, and fixes ldap sync to work with overlapping enrolment periods.
Refs #351: This has evolved into a rewrite of how the LDAP sync works
Refs #351: Adds course group synchronization to LDAP course sync. Updates course audience ldap sync cronjob to work with new sync class.
Refs #351: Adds required constants to settings file
Removes instantiation of class in the header. Fixes the uninitialized SUFFIX variable to use the private property.
Merge pull request #427 from EntradaProject/feature-ldap-sync-updates

Refs #351: Adds ability to sync course group members via ldap, and fixes...
Brings feature-course-objective-dates in line with develop so as to merge branches cleanly.
Adds Don's Models_Base class from the credentialing project.
Merge pull request #422 from EntradaProject/feature-course-objective-dates

Refs #389: Updates course objectives to have start / finish dates
Added the ability to select a numeric minimum passing threshold when importing assessment grades in the gradebook module for a Pass/Fail assessment.
Merge branch 'develop' of https://github.com/EntradaProject/entrada-1x into feature-gradebook-import-csv
Fixed a couple minor issues with the csv uploading changes, to ensure that the grade threshold functionality is "ignored" when not enabled, and that 0 counts as a fail when it isn't enabled, rather than throwing errors.
Ref #283 Added active checks to a few places where the gradebook assignments are being used. It was already being used to deactivate rather than delete assignments, but not every check that could have possibly used it was.
Cleans up aliases in students query.
Merge pull request #433 from EntradaProject/feature-gradebook-import-csv

Feature Gradebook Import CSV Changes
Refs #435, fixes community_notify's permissions query for "post" content types.
Refs #360, allows enrollment in curriculum periods that have already passed.

This just takes off the `finish_date` >= NOW() restriction when selecting a curriculum period.
Refs #303, fixes success message for activating learners in Manage Cohorts.

When activating/deactivating/deleting learners from a group, the repeated message "Successfully activated the selected group member" is replaced by "Successfully activated <name of learner>".

On the Edit Groups interface, the "Delete/Activate" button has been replaced by a green "Activate" button and a red "Delete/Deactivate" button. When the user clicks on one of these it passes their choice via POST (not GET since the form is already submitting via POST) so that on the confirmation page there is either a green "Activate" button or a pair of "Deactivate" and "Delete" buttons, but not both.
Fixes bug whereby Quiz response feedback was being saved regardless of whether the feedback checkbox was checked or not. Refs #362