Previously avatar used SpatiallyNestable scale to keep track of model rendering scale.
It now uses a new member variable _modelScale instead. This is important because the
notion of "Avatar" space does NOT include scale, so this is now reflected correctly in
the SpatiallyNestable class.
Similarly, EntityItems no longer stuff dimensions into the SpatiallyNestable scale
field. a new _dimensions member variable is used instead. The SpatiallyNestable scale
field for entities should always be one.
Parent joints can now have scale if getAbsoluteJointScaleInObjectFrame() returns a non-zero scale.
This is used in the case of the faux SENSOR_TO_WORLD_MATRIX_INDEX joint.
Overlays now ignore the SpatiallyNestable scale, and render using only orientation, position and dimensions.
Added qDebug stream support for Transform class.
