Replace keyguard with new implementation

This change refactors keyguard to be more modular and maintainable.  More
specifically, it replaces the top-level view with just one device-dependent
view that contains two views: a widget area and a security area.

The widget area can be populated with custom widgets.

The security area contains the current security method as dictated by
the stored password quality.

This change contains both the old and the new keyguard with the old keyguard
still enabled.  The new keyguard will be enabled in a subsequent change.

Change-Id: Id75286113771ca1407e9db182172b580f870b612