Recents long press: add pluggable implementation

- Adds a Secure.Setting for the activity component to handle
  Intent.ACTION_RECENTS_LONG_PRESS.
- Adds a new intent ACTION_RECENTS_LONG_PRESS for the
  long press of the recents button. Other system applications
  can register for the intent to provide custom handling.
  Handlers of this intent are queried for in the settings
  application, and if no handlers are found, the default
  implementation falls back on ActionUtils.switchToLastApp().

  The long press listener on the recents button is replaced
  with a touch handler to allow for more custom handling.

For cm-12.0, the following modifications were made:

- With the full deprecation of ActivityManager.getRecentTasks(),
  applications can not query for the last foreground application.
  To aid these applications, the framework will include an
  EXTRA_CURRENT_PACKAGE_NAME with ACTION_RECENTS_LONG_PRESS.
- Instead of re-evaluating packages on every Long Press, PhoneStatusBar
  now tracks Settings changes and package activities and
  incrementally caches the desired Recents long press behavior.

This is a roll-up CR from cm-11.0, and also contains the following Change-Ids:
- I689e8b5c26b39e100cb166d2f93e7ee49e83f93a

Change-Id: I8a27ae0fe58d92a1626f0bd661c5f57c589fac17