Node Split PoC

[pigmej]

This is the prerequisite for #334.

The expected outcome is that:

• node split setup works on testnet
• We have gathered reqs that are needed to write the final implementation
• The expectation is that the setup will be never used on production as completed in the node-split PoC.
• all unnecessary protocols and communication should be removed from the smeshing-service part.
• a tech demo delivered to the community

[jellonek]

With spacemeshos/go-spacemesh#6521 we have confirmed that such setup works on testnet.

Beside that changes included in https://github.com/spacemeshos/go-spacemesh/tree/node-split-poc already have stripped from client side most if not all unnecessary protocols (I'm still trying to confirm that).