Don't rollback a failed interactor

Interactors should be single-purpose. An interactor should not affect
its context until it's performed successfully. This eliminates the need
for cleanup on failure. Only successfully performed interactors within
an organizer will be rolled back.
Fix organizer rollback to properly handle organizers within organizers

To accomplish organizer rollback, we store instances rather than classes
in the organizer's "performed" method so that "performed" for nested
organizers is still intact and available.
Expect no rollback on the failed interactor with nested organizers
Merge pull request #6 from collectiveidea/skip-rollback-for-failed-interactor

Skip rollback for failed interactor