Variable Ledger.params

Consensus-critical constants used by this Ledger

class Ledger
{
  // ...
  immutable(ConsensusParams) params ;
  // ...
}

Expose the ConsensusParams the Ledger is instantiated with. In the main BOSAGORA network, this should be the default-constructed consensus params. However, alternative network (such as TestNet) may use a different set of parameters to achieve different outcome (e.g. different externalization time or staking requirements).