Change demo link to HTTP, to prevent blocking

The link to the demo uses HTTPS, but if you try to load WADO's from external sites served with HTTP, they get blocked. Changing to HTTP seems to do the trick for external HTTP WADO URL's .
added support for generating CornerstoneImageLoadProgress events
updated example to show progress as its loaded
* NOTE - Have not confirmed this actually works yet, but it should based on @jmhmd's example
Merge pull request #2 from simonmd/patch-1

Change demo link to HTTP, to prevent blocking