Merge pull request #9658 from KevinGrandon/bug_867219_single_unlock_step

Bug 867219 - New lock screen implementation r=yuren(cherry picked from commit 83643d05ee93a0f0bb4b3d3239384736514a92d4)

Conflicts:
	apps/system/locales/system.ar.properties
	apps/system/locales/system.fr.properties
	apps/system/style/lockscreen/lockscreen.css