introduced CombinedRU that handels multiple RUs and renders their images together by simple blending (WHITE = transparent). This replaces the same functionality in the AWTImageProvider, that from now only takes one RenderUnit (which may be a combined one). Also changed the OverlayRU to accept other background renderers as well
fixes for RenderUnits   CombinedRU did use the wrong index and didn't treat inactive images correct
moved redraw event to the file panel because that is the point where the (image)source is actually changed
- important for chain of events
edit annotator can now display images or images and labelings with overlays on top
connected reset to the used event service (dummy service before)