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- Added a whitelist permission, to ensure only system
  services (such as NFC) can whitelist MAC addresses.
- Added HANDOVER_STATUS permission, to ensure handover
  transfer status can only be received by eligible services
  (such as NFC).
- Added new confirmation type HANDOVER_CONFIRMED; this indicates
  the transfer was initiated by a handover, and doesn't need to be
  confirmed. This type is also reused to send broadcasts
  to the NFC service, so the NFC service can show notifications
  and deal with the received data.
- Added 15 second timeout to whitelist.
- Modify notication code to not show any notifications for handover
  transfers; instead, send broadcasts to indicate handover status.
- Modify "transfer complete" code to sendbroasts to indicate handover
  status.
Change-Id: I00c08e09eaf44f0bd4bd837cb6b0c37b802742bc