Only _load() viewport ONCE on Rendering Save/reset

This bug was causing setupTiles() to be called mulitiple times, which resulted in
many unecessary tiles being requested by the big image viewer
On rendering settings save, refresh viewer AFTER save

The saveImgRDef request fails in very big images because it happens at the same time as
many tiles are being requested. See http://trac.openmicroscopy.org.uk/ome/ticket/10660