Update SignedMessage (Prereq for crawl and clean)

[tomijaga]

Update SignedMessage (Prereq for crawl and clean)

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Overview

The SignedData type has been depracated now all node request use the SignedMessage type

You should remove all the uses of SignedData from the repo and replace them with the SignedMessage type

Behavior

The SignedMessage interface should be updated to this:

message:{
    crawl: "start" | "stop"
},
node_identifier: 565723676...,
signature: 54cd54bvd...

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[tomijaga]

prerequisite for #91