ViewportGadget : Organise functions into relevant sections
ViewportGadget : Organise functions into relevant sections

The primary motivation is to put the camera functions into separate sections for 2D and 3D cameras, as specified by `setPlanarMovement()`. While some of the 3D methods (e.g.`getCamera()`) might work reasonably in 2D mode, I have deliberately not mentioned that. It's clearer to view the two sections as two completely separate APIs that might one day belong to separate 2DViewport and 3DViewport classes.

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