Tool to display DICOM overlays

When enabled this tool will disable the DICOM overlays stored in `image.overlays`

The overlays data is created by `cornerstoneWADOImageLoader` - see cornerstonejs/cornerstoneWADOImageLoader#239

Implements DICOM standard C.9 - http://dicom.nema.org/dicom/2013/output/chtml/part03/sect_C.9.html

src/index.js

@@ -156,6 +156,7 @@ export { zoom,
   zoomWheel,
   zoomTouchPinch,
   zoomTouchDrag } from './imageTools/zoom.js';
+export { default as overlays } from './imageTools/overlays.js';
 export { brush } from './paintingTools/brush.js';
 export { adaptiveBrush } from './paintingTools/adaptiveBrush.js';
 export { default as version } from './version.js';