Implement APIs to store and index blocks and provide block-related endpoints

[franklywatson]

This issue continues breaking down the formal Ethereum RPC spec into dependency ordered chunks. This issue groups a set of APIs which store and index blocks and provide block-related endpoints.

• eth_getBlockByHash
• eth_getBlockByNumber
• eth_getBlockReceipts
• eth_getBlockTransactionCountByHash
• eth_getBlockTransactionCountByNumber

We will need to:

Understand the internal wiring to be implemented and what interactions with BridgedAccount or other Flow constructs this will have in the functions implementation. Formalize the specification/requirements through discussion in this issue
Implement the endpoints above including corresponding automated tests to the agreed upon spec

[m-Peter]

I will open a follow-up PR for eth_getBlockReceipts.