Add SIS ID column to Gradebook2

Implements this feature request:

> https://help.instructure.com/entries/22800435-Add-an-SIS-ID-student-number-column-to-Gradebook

Test Plan: Verify that the SIS IDs displayed in Gradebook2 are accurate, searchable (filterable), and sortable.

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*NOTE: We have a signed CLA for all of Simon Fraser University (SFU) on file.*