This adds the global accumulated refund counter to the standard
json output as a numeric json value. Previously this was not very
interesting since it was not used much, but with the new sstore
gas changes the value is a lot more interesting from a consensus
investigation perspective.
Makes Interface interface a bit more stateless and abstract.
Obviously this change is dictated by EVMC design. The EVMC tries to keep the responsibility for EVM features totally inside the VMs, if feasible. This makes VM "stateless" because VM does not need to pass any information between executions, all information is included in parameters of the execute function.
