Relationships mirroring

[bronenos]

Public overridable Object's extension for relationship mirroring to be able.

Example:

extension Product {
  override func rrc_mapObjectToMirror() -> Product {
    let clone = super.rrc_mapObjectToMirror() as! Product
    clone.category = self.category?.rrc_mapObjectToMirror() as? Category
    return clone
  }
}

[polqf]

Hi @bronenos,
Thanks for this PR.

Could you move the method to ObjectExtension.swift ?
Also if you can rename it to something like getMirror, would be great. We don't believe in prefixes since Swift appeared.
I think that with this change the current getMirror top level function makes no sense, so probably its implementation should be now inside the Object Extension method

[bronenos]

Okay, done

[polqf]

Hi @bronenos , merging it right now, I'll fix the tests Travis is complaining about