Setting timestamp based on number of samples sent

- Added timeStamp property to EncodedAudioPacket
- Added timeStamp parameter to rtpPackageWithDefaults constructor
- Added nextTimeStamp to AudioPacker with random initial value and sample length increases
- AudioSocket forwards timeStamp
- Added generateSecureRandomUInt32 to CryptoTools
- Updated tests
FREEBIE

Fixes https://github.com/WhisperSystems/Signal-iOS/issues/143 but not https://github.com/WhisperSystems/Signal-iOS/issues/144