Updated backlog/roadmap
Improved naming for image loading:
  loadImage() now just loads the image and does not cache it
  loadAndCacheImage() loads and caches the image
updated examples to use new
beta 1 build
updated readme to reflect beta status
Got rid of CornerstoneViewportUpdated event since CornerstoneImageRendered does the same thing

 CornerstoneNewImage is now emitted before CornerstoneImageRendered when an image is changed

 versions bumped for beta 2 release