Add content_script to forcefully stop page loading before sray has a cha...

...nce to process

* background.js
  - Add code to return to caller whether the background.js script has intercepted a tab's url for sray processing before
* popup.js
  - Renamed port to be more descriptive
* manifest.json
  - Add content_script stop.js
* stop.js
  - Forcefully stops page loading using window.stop() to give sray a chance to examine/process the page
* known issue
  - Changing the url on a page that has sray processed before results in a loop