`theta_jn` and `iota`

A discussion arose in !266 (merged) that we interchangeably use iota and theta_jn. I believe iota is typically referred to in most publications, but perhaps internally theta_jn is inline with lalsimulation (correct me if I'm wrong).

Marking this issue as a point of discussion how we should handle this. Currently, iota is the user-facing parameter, but internally we refer to theta_jn. What are peoples thought? Happy with it as-is or should we change wholesale?