Why

Reduce boilerplate and have cleaner code. This is also a first step into achieving better memory profile for hydra-node #1618

What

• Remove ServerOutput type and add/create constructors in StateChanged (Most ServerOutputs directly map to a StateChanged event, Some additional events need to be created to server outputs like PeerConnected et al)
• Instead of cause ClientEffect, the HeadLogic would emit events with newState.
  Example:

  hydra/hydra-node/src/Hydra/HeadLogic.hs

  Lines 599 to 600 in f770319

  	newState SnapshotConfirmed{snapshot, signatures = multisig}
  	<> cause (ClientEffect $ ServerOutput.SnapshotConfirmed headId snapshot multisig)

  
  would become

  newState SnapshotConfirmed{headId, snapshot, signatures = multisig}