Allow staff to create reservations before a student's first sign-in

[mwest1066]

Staff may need to create or assign an exam reservation before a student has signed in to PrairieTest for the first time.

Questions:

• What workflows or use cases require creating a reservation before the student's first sign-in?

Originally raised in discussion #118.

[ffund]

Our use case for this is:

• We have some exams where staff places students in sessions rather than letting them place themselves, e.g. all students in a particular section might take exam at their regular meeting time.
• We want to set up the session, make reservations for the students who have to be in that session, and then open the rest of the seats for general use.

However, if the students who are going to be "placed" by staff haven't signed in yet, we can't do that all at once. We have to keep going back to that exam, checking which students are newly signed in, adding reservations for them, and re-adjusting the capacity for general use. It becomes a "daily" task instead of a one-time task.