Merge pull request #23118 from davidflanagan/bug1051172-v2.0

Bug 1051172: a stoprecording event hack so the camera can stop recording more quickly on app transitions. r=kgrandon,justindarc a=2.0+(cherry picked from commit 4ea69f01f52f472331d12b001ec1e37631bff575)

Conflicts:

	apps/camera/index.html
	apps/camera/js/app.js
	apps/camera/js/config/require.js
	apps/camera/js/controllers/camera.js
	apps/camera/test/unit/setup.js
	apps/system/js/app_window_manager.js

remove unused listenForAttentionScreen function
Merge pull request #23214 from davidflanagan/bug1051172-v2.1

Merge pull request #23118 from davidflanagan/bug1051172-v2.0