SystemUI: Add CM statusbar item holder

*) Backport to cm-14.1

*) To be used as a layout to hold one or more cmsdk status bar
   feature classes.

*) Propagates visibility and tint information via interfaces
   defined in cmsdk internal.

*) Supports adding further interfaces without impacting existing use
   cases.

Change-Id: I3b98837e076ba1cb0d4ca6e7588c1e917f81e65a