Add net and web3 namespaces

[m-Peter]

Description

Adds the following JSON-RPC endpoints:

• net_listening
• net_peerCount
• net_version
• web3_clientVersion
• web3_sha3

web3.js makes use of some of the above.

Documentation with instructions on running the gateway locally as added, as well as a list of ready JSON-RPC calls to executed.

---

For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels