Reorganized SceneCache parms.

Moved Push button and all the options it effects to a new Options tab
Added attributeCopy option parm (used in next commits)
Pushing the attributeCopy parm when expanding SceneCache OBJs
Creating struct for SceneCacheSource parms to avoid function bloat
Using attributeCopy parm to modify the loaded object before converting to Houdini.
fixing spelling mistakes
Merge pull request #167 from andrewkaufman/pref

Houdini Attribute Copy for SceneCaches