Improve LTI 1.3 integration - option to not auto assign sets to students

[andrew-gardener]

• Add an option at the course level to disable auto assigning all available sets to everyone.

Consider when this is on if

• not sets should be assigned to anyone ever (so instructor must manually manage this completely)
• auto assign to the set that the user launched into (so instructor might not need to manage completely but could cause issues if restrictions are not placed in the LMS for the link)

[andrew-gardener]

Mech2 would need this by Sept 2021