Implement waku/0 - current Status whisper fork as is

[kdeme]

Implement waku/0 protocol, a Status fork of Whisper implementing the additions/changes done to it.

This will mostly be adding message packets ids, changes to light client (not sure?), notification on send (how does this work now? and why?). Questions should be asked regarding the validity of changes (is everything still used and needed?).

Mailserver related changes are targeted in separate issue: https://github.com/status-im/nim-eth/issues/102

Requirements:

• Changes done by Status should be well documented (e.g. at https://github.com/status-im/specs/ ).
• Refactor whisper message structure + protocol code #122

Acceptance: Implement Status go compatible waku/0.

[oskarth]

@kdeme what's left / most prio in this? Hard to see at a glance what's missing

[oskarth]

Mailserver client WIP PR for easier reference #141

[kdeme]

What is left I think is:

• Light client allowed to send through regular messages packet
• Message confirmations part, although that part makes actually only sense for mail client / server communications.
• Perhaps any of those other added (and not fully explained) protocol packets. But I think all relate to mail client / server implementations and are probably not even necessary.

[kdeme]

This is mostly done now.

What is missing is mail server, but that has a separate issue. And confirmations are not implemented, as they are directly linked to mail server (only used there). The setting at Status packet is added however to be compatible.

Compatibility however will probably not be OK for now as there is also the Waku Mode PoC that is already added: see #124