Integrate eth_accounts and eth_transact to use new account manager

* Add from to eth_transact / xeth.Transact and add static pass in lieu
  of integrating with native Mist window for user passphrase entry
* Make eth_accounts return AccountManager.Accounts()
* Add a Generate Key menu item in Mist

core/types/transaction.go

@@ -129,6 +129,7 @@ func (tx *Transaction) sender() []byte {
 	return crypto.Sha3(pubkey[1:])[12:]
 }
 
+// TODO: deprecate after new accounts & key stores are integrated
 func (tx *Transaction) Sign(privk []byte) error {
 
 	sig := tx.Signature(privk)
@@ -140,6 +141,13 @@ func (tx *Transaction) Sign(privk []byte) error {
 	return nil
 }
 
+func (tx *Transaction) SetSignatureValues(sig []byte) error {
+	tx.R = sig[:32]
+	tx.S = sig[32:64]
+	tx.V = uint64(sig[64] + 27)
+	return nil
+}
+
 func (tx *Transaction) SignECDSA(key *ecdsa.PrivateKey) error {
 	return tx.Sign(crypto.FromECDSA(key))
 }