Integrate with rules and/or ECA

It would be really helpful having a non-dependent integration with Rules, such that when someone accepts an agreement we can invoke a custom rule event, passing along the user who accepted and the agreement type they accepted, so that we can assign roles to those users automatically, as an example.

This integration can be non-dependent by wrapping any rules specific calls into module_exists() calls.

We will need a custom rule event and rule condition (so we can compare which agreement the user accepted, thus allowing us to assign separate roles depending on the agreement).