* Made the Basis euler orders indexed via enum.
* Node3D has a new rotation_order property to choose Euler rotation order.
* Node3D has also a rotation_mode property to choose between Euler, Quaternion and Basis
Exposing these modes as well as the order makes Godot a lot friendlier for animators, which can choose the best way to interpolate rotations.
The new *Basis* mode makes the (exposed) transform property obsolete, so it was removed (can still be accessed by code of course).
