Implement state sync strategy

[dimartiro]

When the warp sync finished getting the fragments and its completed, we need to request and import the latest state.
This is a task that could take time and needs its own logic to be handle correctly.
For this reason we are not going to implement the state sync as part of the warp sync, instead, we are going to implement it as an independent strategy that might be run right after the warp sync strategy finished.

• OnBlockAnnounceHandshake: Will update the best block hash / number for that peer
• OnBlockAnnounce: same than OnBlockAnnounceHandshake
• NextActions : Will return a state request
• Process: Will process the response and import the state

We can read more about how the state sync is started after warp sync finishes here

An idea of how to implement the state sync strategy based on parity's implementation is here