AddStudents Controller

[jackmacdougall]

Create a controller for adding students to groups

• [ ] Should be able to have students add themselves to a group
• [x] Instructor should be able to add students to group
• [ ] There should be multiple groups that students can be added to

[LMacGillivray]

Currently have the ability to add students via endpoint addStudents.

To implement

• assignStudents endpoint for instructor
• multiple groups to be added

[LMacGillivray]

New process of slices makes issue invalid, closing