evm integration for transaction execution

[arcolife]

to facilitate payload execution, we need compiler integration. Related to #31

cc/ @samikshan

[arcolife]

func (nd *Node) execute(am ApplyMsg) {	
	// TODO: add msg to applyCh, should be executed in a separate go routine	
	// TODO: add we probably want to keep a log for this	
	nd.ApplyCh <- am	
}

..is the bane of transaction execution right now. Removed in #61 but needs to be brought back in this issue.