Removed deprecated app window singleton attribute
Merge branch 'removeSingleton' of https://github.com/beaufortfrancois/chrome-app-samples into beaufortfrancois-removeSingleton

Conflicts:
	README.md
	samples/singleton/README.md
	samples/singleton/assets/screenshot_1280_800.png
	samples/singleton/assets/screenshot_thumbnail.png
	samples/singleton/icon_128.png
	samples/singleton/icon_16.png
	samples/singleton/main.js
	samples/singleton/manifest.json
	samples/singleton/singleton.html
	samples/singleton/singleton.js
	samples/singleton/singleton.png
	samples/singleton/styles/main.css
Merge branch 'beaufortfrancois-removeSingleton'