Added setMFJson(mfjson) and setMF(st, et, x, y, w, h) methods to smfplayer to dynamically set the media fragment to be displayed. setMFJson sets it raw, and setMF takes in pre-normalized values in seconds for temporal and percent as spacial unit. setMF can be called without spacial args to just set the time params, or with time elements -1 to only set the spacial params.