Bug 971498 - [System2] Instantiable HomescreenLauncher

Conflicts:
	apps/system/js/homescreen_launcher.js
	apps/system/test/unit/app_window_manager_test.js
	apps/system/test/unit/bootstrap_test.js
	apps/system/test/unit/homescreen_window_test.js

Bug 979212 - Require MockHomescreenLauncher in unit test of EdgeSwipeDetector

Conflicts:
	apps/system/test/unit/bootstrap_test.js