core, consensus: pluggable consensus engines (#3817)

This commit adds pluggable consensus engines to go-ethereum. In short, it
introduces a generic consensus interface, and refactors the entire codebase to
use this interface.

cmd/evm/disasm.go

@@ -20,10 +20,10 @@ import (
 	"errors"
 	"fmt"
 	"io/ioutil"
+	"strings"
 
 	"github.com/ethereum/go-ethereum/core/asm"
 	cli "gopkg.in/urfave/cli.v1"
-	"strings"
 )
 
 var disasmCommand = cli.Command{