- added "manual" tests for amf (not zipped) loading
 * added experimental resizing support for multi object loaders (like amf loader, since there is not a single geometry only)
 * added experimental computeObject3DBoundingSphere method to get bspheres of meshes (vs the usual bspheres of geometries)
- various minor cleanups :
 * resource loading on-screen messages get removed once a resource is fully loaded