libp2p integration for private networks

[sambarnes]

The homegrown p2p package in factomd works well enough for mainnet, but can not be quickly iterated on due to backwards compatibility requirements with nodes you do not control. In the setting of a private network where you control all the nodes, we can offload network layer responsibilities to modern libraries such as libp2p.

Steps:

• Investigate libp2p usage in other python projects (e.g. Trinity or a py-ipfs)
• Abstract away existing p2p code (if still needed) to seamlessly switch between traditional factomd p2p and libp2p
• Integrate libp2p