Adds useful_script to change room capacities and move classes.

For example, if you want to do a bunch of changes at once while a reg is
open.
Adds some stuff to class capacity setting script.

Makes it possible to do room swaps, and marks classes as accepted.
Makes minor improvements to class capacities script.
Merge pull request #661 from benjaminjkraft/change-capacities-script

Adds useful_script to change room capacities and move classes.