Freebird: the new go-recurly plugin

mostly pulled out of `go-subscriptions` and `go-subscriptions-freebies`.

see https://github.com/GigaOM/legacy-pro/issues/4125
I'm unsure about this being in `go-recurly` as opposed to `go-subscriptions`.  All the conditions are based on the return values for `go_subscriptions()->get_subscription_meta( $user_id );`  It would seem like either that function should be moved here, or this function moved there.