Add StateRoot message

[ZhangTao1596]

Add StateRoot message support in core.

• Node relay StateRoot when there is no MPTPlugin.

[shargon]

Does we need states without witness?

[ZhangTao1596]

Yes. The state root calculated locally has no witness.

[shargon]

Maybe we should have two payloads, signed and unsigned, in order to prevent send of unsigned state roots.

[ZhangTao1596]

I add witness null check. But how can extra payload prevent sending unsigned roots?

[shargon]

We will send and receive only signed roots, the unsigned payload will be used locally, without p2p message.

[ZhangTao1596]

I want to store StateRoot with null witness first. After validated StateRoot received, I can replace the null witness with signed witness.

[shargon]

We will have the message in the core and the logic in modules?

[ZhangTao1596]

We will have the message in the core and the logic in modules?

I have thought of put all into plugin. But in that case message will only relay between node with specific plugin. It will not work, nodes with specific plugin are minority.

[Tommo-L]

As #2101 , this pr need to be moved to neo-modules.

[ZhangTao1596]

Will move to plugin.