Refactoring all apps search to support external search bar.

- Adding support for an external search bar that can be used
  to search a container view.  This adds a new interface
  AllAppsSearchController which manages the external search
  bar.  Each controller will have its own search implementation
  which means that we no longer need a common AppSearchManager
  interface.
- Removing elevation controller as we no longer have a builtin
  search bar in all apps
- Refactoring container view insets so that they behave
  the same in all containers.
- Refactoring apps view to ensure that we only update the number
  of columns with the available width
- Cleaning up LauncherCallbacks interface

Bug: 20127840
Bug: 21494973

Change-Id: I710b8e18196961d77d8a29f0c345531d480936fe