Unify all services in full-node/light-base to the same paradigms

[tomaka]

I've experimented a lot over time on how to design the various services.

I think that the best design, in terms of ease to follow is:

• One background task, which we communicate with only through channels.
• No small child tasks, as it's a bit complicated to reason about the task shutting down. FuturesUnordered is fine. The only accepted child tasks are for the networking service, so that it doesn't crash if a child task crashes.
• One giant loop plus match block with all the wake up reasons. No code above or below this pattern.

All the services should be tweaks to conform to this:

• full/network
• full/network/tasks
• full/consensus
• full/json-rpc
• light/network
• light/network/tasks
• light/sync/relay
• light/sync/parachain
• light/runtime
• light/transactions
• light/json-rpc