[Enhancement] Allow instructors to message students from the help modal

[y2kmurali]

I usually click the "help" button on the queue before attempting to join a student's meet (so that no other instructor tries to join at the same time), but that means that if I need to message the student to let me into their meet/it's expired, I have to first click one of the "helped" or "not reachable" buttons- if I clicked the wrong one (e.g. they were in their meet and I clicked not helped, or vice versa), it's hard to rectify it (in the example provided, I'd have to pin and then press help again to get rid of their priority).

It would be nice to provide the ability to message students directly from that modal, so that the workflow becomes streamlined. Another option would be to do something like #8 to allow pinning to be used as a "staging area" for students that are in the process of being helped, at which point we can just send a message from the queue directly.