Add Speculative Execution for livenet deploys.

[Maciej Zieliński]

[Maciej Zieliński]

Try to catch 'speculative_exec' is not a supported json-rpc method on this server and then communicate gas need to be set manually.

pub enum GasStrategy {
   SpeculativeFirst,
   ManualIfSetThenSpeculative,
   ManualFirst // skips sepeculative
}

Maybe add livenet_env.set_gas_strategy(GasStrategy::ManualOnly)