Allow a model to be both a parent and child

[chadhutchins]

The only reason this didn't work previously was due to duplicate method names in HasParent and HasChildren traits.

We have a use case where we have several layers of abstraction:

A extends B B extends C

With this change we can now:

A HasParent B HasParent, Has Children C Has Children

and by C::find('1234') will return the class instance of A correctly.

[tobias-grasse]

@driftingly Is there something to be done before this can be merged? I'd be interested in this functionality, so I'd be glad to help.

[driftingly]

@tobias-grasse If you're able to, tests would be helpful.

[driftingly]

I ran this update through the test suite of a larger project and didn't run into any issues.