Merge remote-tracking branch 'upstream/master' into bubble-tea

Conflicts:
	apps/system/js/app_window_manager.js
	apps/system/js/cost_control.js
	apps/system/test/unit/app_window_manager_test.js
	apps/system/test/unit/bootstrap_test.js
Revert "Merge remote-tracking branch 'upstream/master' into bubble-tea"

This reverts commit 2305c9f8924bbb162600d97da36d2c047ee61210, reversing
changes made to 20954fbbe8e6b3761d9e55caf485220399fbf202.
Bug 979212 - Require MockHomescreenLauncher in unit test of EdgeSwipeDetector
Bug 979750 - [System2] "attention_screen" and "media_recording" missing "Applications"
Merge pull request #16892 from mpizza/Bug_979750

Bug 979750 - [System2] "attention_screen" and "media_recording" miss "Applications".
Merge pull request #16818 from dwi2/bug979212

Bug 979212 - Require MockHomescreenLauncher in unit test of EdgeSwipeDet...
Bug 897352 - [gaia build system] Transition to a build_stage for assembling apps
Modify commit accroding by first round review
WIP 3/6
fix manifest error for keyboard app
minor fixes
fix preload apps issue