Adjust iconography in notification guts.

  (i) is now the system's app notification info panel,
      allowing you to block, prioritize, and things like
      that.

  (gear) is new; it will appear only if your package has a
      notification settings activity of its own. If the user
      taps this you'll be launched with some useful extras:
      notification_id and notification_tag, matching the id
      and tag of the notification the user longpressed.

Bug: 17005733
Change-Id: Ib09264c2564152ab27e744c47ed87a0e9223656f