Added instrumentation to Photo pixbuf pipeline to measure absolute time of each stage.  Also added feature to 
allow caller to declare a scale for the pixbuf; Photo can perform the scale at an opportune time and reduce 
overhead in certain operations.  Also fixed bug where the Thumbnail objects in the entire system were being 
resized when the slider moved; now, only those that are in view are resized, and the others resize when they 
come into view.