Redesign DIY Blockchain

[delventhalz]

The DIY Blockchain should be redesigned to minimize unnecessary noise and re-order tests to be based around implementing functionality rather than per-module. For example the signing module should be started as a part of building transactions, not front-loaded with no context.

Rough order:

• Blocks and Blockchains: includes hashes and block validation, should be able to handle any data (either a string or an array of transactions)
• Transactions: includes signing and validation of transactions
• Consensus (Extra Credit): mining, balances, additional validation