Allow TAs to claim students as part of their sections

[damianhxy]

For CMU, instructors do not want to manually update each section roster. However, the lecture roster lists the lecture number in the section field. This leads to many courses being misconfigured for TAs.

It would help to allow TAs to select students (e.g. on manage course users page) and claim the students as part of their sections, i.e. update the lecture and section details for those students.