Generate MetaEvidence and Add to IPFS

[satello]

Upon submission of the transaction MetaEvidence should be generated and included in the transaction. Can use same MetaEvidence as is used with escrow.

Evidence display interface can be found here: https://github.com/kleros/escrow-evidence-display

escrow-react/src/index.tsx

Line 71 in 4394ff4

// TODO generate meta evidence and add to IPFS