Bug 937442 - (lockscreen-window) [Window Management] Implement LockscreenWindow to manage LockScreen.

Conflicts:
	apps/system/js/lockscreen.js
	apps/system/test/unit/bootstrap_test.js
	tests/python/gaia-ui-tests/gaiatest/tests/functional/lockscreen/test_lockscreen_unlock_to_emergency_call_screen.py
Merge pull request #17835 from snowmantw/issue937442-lockscreen-window

Bug 937442 - (lockscreen-window) [Window Management] Implement LockscreenWindow to manage LockScreen.