SceneCache SOP Performance and Consistancy

The first commit improves performance of the SceneCache SOP by finding all named primitive ranges upfront before recursing through the hierarchy. This relatively expensive loop was added in 8.0.0-b2 because it improved load times, but unfortunately it destroyed animation times. The new approach brings the animated performance back inline with 8.0.0-b1, while maintaining (if not improving) the on-load performance from 8.0.0-b2. See the commit message for some stats.

The second commit makes the node give consistant results across Houdini sessions by sorting the children by name before converting them. This actually reduces the performance a bit since (though in testing it was a relatively negligible bit). The last commit just adds a todo to InternedString to think about providing string based sorting by default.