cmsdk: Add CMStatusBarItem interfaces

*) Backport to cm-14.1

*) Introduce CMStatusBarItem class that contains interfaces
   and utility methods that can be used by status bar items that
   that are hosted here in the cmsdk in order to communicate
   with systemui.

*) Nested interface: Manager
   Implemented by layout view CMStatusBarItemHolder in systemui.
   Contains methods that are used to request receipt of certain
   systemui events.

*) Nested interface: VisibilityReceiver
   Can be used to listen for changes in visibility of a statusbar item.
   Works even if the statusbar item sets it's own visibility to GONE.

*) Util method: findManager(View v) walks up through parent views to
   look for something that implements Manager.

*) Systemui side that provides a layout that implements Manager:
   CMStatusBarItemHolder

Change-Id: I6d93bb492612ad03e41d60197b33a7379c9f21b0