demo: blockchain, p2p and wallet integration

[oleganza]

Currently, blockchain is processed internally and stored alongside wallet data. We need to move it under the ownership of the p2p part, and store it separately from the wallet/accounts data. UI will communicate with p2p part over mpsc channels to request current status, spendable utxos (#426) and submit transactions.

We should probably use 3 separate DBs for blockchain, index and wallet data.