accounts, core, eth, xeth: use account manager for everything

The account manager is now responsible for picking the
default account and the coinbase.

core/manager.go

@@ -1,7 +1,6 @@
 package core
 
 import (
-	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/ethutil"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/p2p"
@@ -14,7 +13,6 @@ type Backend interface {
 	PeerCount() int
 	IsListening() bool
 	Peers() []*p2p.Peer
-	KeyManager() *crypto.KeyManager
 	Db() ethutil.Database
 	EventMux() *event.TypeMux
 }