Keepalive monitor should be its own package

[mercul3s]

We need to implement monitors in eventd for check ttls, so we should refactor it into a backend package and update keepalived to use this package. We'll also need to implement a version of EventCreator in eventd for creating check ttl events.

[mercul3s]

After investigating this, EventCreator functionality should instead be rolled into Keepalived and Eventd and handlers created for updates and failures in Monitor, with an interface for accessing them.