Make session host portable

[drewyoungren]

As I understand it, right now host credentials use localStorage when starting a session. I would like to have a way to get those credentials onto another machine, like, say, a classroom computer for presenting.

A simple solution, I think, is to just make a hostKey=${someUniqueString} entry into the URL search string. The polls could then be set up before class and broadcast/collected from the classroom.