Node input buttons (e.g. in the material properties) used to draw their
icons on the right of the buttons. However since they represent inputs,
it makes more sense conceptually to have them on the left.
Further, we might want to add the usual decorator buttons (to control
keyframes or display other states) to the material properties as well.
Having two circle icons next to each other would be confusing.
Differential Revision: https://developer.blender.org/D7409
Reviewed by: Brecht Van Lommel, William Reynish
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