Implement setActivityLabelAndIcon().

Replaces Activity.setRecentsLabel and Activity.setRecentsIcon.
Simple top-down traversal to find the highest activity with a
specified label and icon. Adds the Intent of that activity to
RecentTaskInfo as well so that Recents can get the launcher
icon if UX desires it.

Fixes bug 13675322.

Change-Id: I62d7d8f4df4dc81012f451e0cdea8a2943aedeec