remove dead SensorInfo code
Several changes

- make rerp() a method on DataSet after all. (I've been going back and
  forth on this. What finally tipped me over is the trivial but
  annoying issue where if rerp() is a fundamental function, then we
  can't use the name 'rerp' for a variable without collisions.)
- rename the event_query arguments to "restrict" from "subset", which
  seems clearer.
- new comprehensive tests for rERP prediction