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.

[damianhxy]

Closing this until class requirements are better understood.

Some thoughts / comments

• Even with this feature, it would be moot if sections are overwritten everytime the instructor re-uploads the lecture roster. Perhaps we should look into supporting multiple section rosters at once.
• With the release/unrelease grades feature (#2081), TAs can manually release grades as they grade submissions if they so wish. This feature might not provide any value-add as a result.
• For some classes (e.g. 18-213), conventional sections are not used and can fluctuate throughout the semester. This would require an "unclaim" feature, at which point we might as well allow uploading of some kind of section roster.