The signature of the `Raw` methods has been changed so that they return
the application messageID.
Clients will keep track of this ID and receive a notification through
the envelopesMonitor of the state of the envelopes (sent/expired).
Envelopes monitor is passed this ID as well.
We use an array of IDs as datasync messages might be batched.
This commit adds the ability of reading and sending datasync messages.
Datasync messages are batched, so a single whisper message might
contain multiple protocol messages.
Datasync messages are parsed regardless of whether the datasync flag is
on, as this commit is backward compatible.
Sending messages is toggled off by default.
Pedro Pombeiro
Adam Babik
Andrea Maria Piana
Adam Babik