Add a way to broadcast signatures onchain

[colin-axner]

Problem

There currently exists no way to send confirmation signatures to all nodes without spending the utxo's.

Proposal

This can be implemented in the same way as `include-deposit`, though I think users should still have the option to spend utxo's without confirm signatures being broadcasted first.

[hamdiallam]

Also requires a design doc/spec before implementing regarding how this fits into the data store.

[wesgraham]

Thoughts on implementation approach below.

Sample Usage:

./plasmacli tx broadcast-sigs ./plasmacli tx broadcast-sigs <input1, input2> ./plasmacli tx broadcast-sigs --confirmSigs0 --confirmSig1

Broadcasting Steps as follows: 1) Retrieve confirm sigs from local storage (iterating over inputs - accessing via clistore) 2) Parse confirm sigs (checking for --confirmSig flag usage overwriting confirm sigs) 3) Create new sigMsg containing confirm Signatures 4) Validate sigMsg 5) Broadcast using cli.BroadcastAndAwaitCommit()

Validate sigMsg includes: { plasma.Input1 plasma.Input2 }

Handling Steps as follows: AnteHandler defines sigMsgHandler 1) Retrieves sigMsgSigner 2) Validates Inputs 2a) validateConfirmSignatures() already exists

• Checks signer of confirmhash = signer of sigMsg

Add route for sigMsgHandler 1) Receives validated sigMsg 2) Stores Signature type in DataStore - contains {signature, inputs, signer}

@hamdiallam would appreciate insight on other things needed here

[hamdiallam]

We don't need the signer because we want to allow anyone to broadcast the confirm signature. The ante handler would check that the confirm signature is correctly constructed.

Looks good to me