CanvasItemEditor Changes:

* Removed the Bone and IK code, which simplified the class quite a bit and removed some signals and functions that were being called routinely.
* Now Bone2D is the only bone (or bone-like thing) in 2D, making it less confusing to know what bone is being used where.
* Removed a few of the Bone dropdown options - Like "clear bones" and the IK related options - as they are no longer needed or usable.
* Reimplemented the "show bones" option, so it shows/hides all of the selected Bone2D nodes and any child Bone2D nodes.
* Reimplemented the "Create Custom Bone(s) from Node(s)" option, which is now called "Create Custom Bone2D(s) from Node(s)"
  * It works okay for nodes that are selected and have no children, but it currently is broken for everything else. I still need to work on it.

Bone2D Changes:
* Added a boolean for toggling whether the editor gizmo is drawn or not. This boolean is a visible property, but only in the Godot editor.