Batch accept users via search queries

[krubenok]

It would be unbelievably helpful to be able to batch admit users from the search queries in the user panel. This would require that the search interface be improved so that selections can be made based on Major, Degree, School, or any other parameters in the application then being able to select all students that match the search criteria or simply select them from the list.

We didn't have time to build this for McHacks, but I did add in a CSV export in the Users list view so we did all of this offline.