Bug 907013 Implement AppWindowManager + AppChrome

Conflicts:
	apps/system/js/homescreen_window.js
	apps/system/js/window_manager.js
	apps/system/js/wrapper_factory.js
	apps/system/style/system/system.css
	apps/system/style/zindex.css
Bug 907013 - Part 2: Unit tests + Integration tests