Made render sphere offsets be relative to the ship instead of the submodel, and implemented a similar $box_offset property for detail boxes.

git-svn-id: svn://svn.icculus.org/fs2open/branches/zookeeper@9990 387891d4-d844-0410-90c0-e4c51a9137d3
Removed the unused Interp_render_sphere_offset variable.

git-svn-id: svn://svn.icculus.org/fs2open/branches/zookeeper@9991 387891d4-d844-0410-90c0-e4c51a9137d3