WhisperPush: allowing whitelisting of needed framework permissions

WhisperPush requires certain framework permissions around SMS
receipt and sending. In order to allow the WhisperPush apk to be
updated separately from the system, those permissions are marked
eligible for whitelisting to a specific signature.

Change-Id: I8b65b42b78b2d8aab6601d5c8a109b1c7005ad2e
(cherry picked from commit e52c239d)