Bug 1059813: Wrap socket I/O operations in |UnixSocketRawData|, r=qdot

This patch moves the I/O operations for sending and receiving data
in |SocketIOBase| into |UnixSocketRawData|. This change allows to
add a clean interface to |UnixSocketRawData| and later replace the
class by other implementations.
Bug 1059813: Use getter/setter methods of |UnixSocketRawData| in |KeyStore|, r=chulee,qdot
Bug 1059813: Use getter/setter methods of |UnixSocketRawData| in NFC helpers, r=allstars.chh
Bug 1059813: Use getter/setter methods of |UnixSocketRawData| in RIL helpers, r=vyang
Bug 1059813: Use getter/setter methods of |UnixSocketRawData| in Bluetooth, r=btian
Bug 1059813: Protect access to fields of |UnixSocketRawData|, r=qdot

This patch adds protection for fields of |UnixSocketRawData| by
making them private.