Offset percentage of actors

This branch ensures that when we turn on `Feature A` for `5%` of actors and turn on `Feature B` for `5%` of actors, the set of actors for which each feature turned on is not *exactly* the same.

This is fixed by using an offset based on the feature's name. Simple fix, but is effective.

Note: Specs for this may note belong where they are now; they may very well belong in `integration_spec.rb`. Can address if necessary.