Add support for object backed link types

[lharris-palantir]

Would be nice to have better syntax for creating object backed links.
E.g. currently if we have a simple link type between person and email, we can create a link in one line personObject.email.add(emailObject)
If we change that to an OBLT (e.g. with an intermediate phone object type), we then need multiple lines of code to create the intermediate object:

let linkObj = Objects.create().phone("test_id")
linkObj.email.add(emailObject)
linkObj.person.add(personObject)

...
ideally we would just do something like personObject.emailPhoneLink.add(pk, emailObject) .