This PR proposes a simple change to `RigGeometry` `dirtyGLObjects` logic.
1. We will avoid dirtying unmodified arrays.
2. We can drop an osg version guard since `Drawable::dirtyGLObjects` is not nearly as harmful as `Geometry::dirtyGLObjects`.
3. We will avoid crashes in an as yet unfinished future PR concerning `Array` sharing improvements.
Double buffering, custom bounding box and the update in the cull visitor (instead of update) are now all handled internally rather than needing hacks and/or callbacks.
