Core actions integration: Add back support for the 'behavior' key, save explicitly all entities that need to be saved (as specified through behavior).

Use operation type 'entity' instead of 'system' for actions that work on all entity types. That matches the Rules terminology.

Pass the full entities when aggregating results for an action, not just the ids (since everything is already loaded anyway). Tweak the 'pass ids to url' and 'execute script' actions a bit.