Bug 971554 - [System2] Instantiable SoundManager

Conflicts:
	apps/system/js/bootstrap.js

Conflicts:
	apps/system/test/unit/bootstrap_test.js
	build/jshint/xfail.list
Merge pull request #17494 from gasolin/sheriff971554

Bug 971554 - [System2] Instantiable SoundManager, r=alive