[WIP] Add offline-first code and contract database (ThreadDB)

[kwingram25]

Placeholder WIP PR for transitioning Canvas UI from localStorage to offline-first ThreadDB P2P back-end for storing code bundles and deployed contracts

JS-ThreadDB overview

Roadmap

• Use offline-only DB for local and development chains (effectively identical to current version)
• Use syncing remote DB for public chain endpoints i.e. Canvas Test
• Add public-key identities for users to allow retrieval of codes/contract bundles from other devices (docs)
• Support sign-in using Polkadot browser extension