Added support for RectTransform

[ryanmeasel]

• The recttransform component throws a warning (as of Unity 4.6) when you set their parent via the transform property transform.parent:

"Parent of RectTransform is being set with parent property. Consider using the SetParent method instead, with the worldPositionStays argument set to false. This will retain local orientation and scale rather than world orientation and scale, which can prevent common UI scaling issues."

• To circumvent this warning, we check if the parent has a RectTransform
  component and set the boolean worldPositionStays accordingly.
• Before calling GetComponent on the parent, the parent must be
  checked for existence.
• Doing so in this manner allows setting the parent transform without changing the local position, rotation or scale. For RectTransform, it also doesn't change the sizeDelta.