wizard: move GoBack from Qt wizard to base_wizard

gui/qt/__init__.py

@@ -41,6 +41,7 @@ import PyQt5.QtCore as QtCore
 from electrum.i18n import _, set_language
 from electrum.plugins import run_hook
 from electrum import WalletStorage
+from electrum.base_wizard import GoBack
 # from electrum.synchronizer import Synchronizer
 # from electrum.verifier import SPV
 # from electrum.util import DebugMem
@@ -48,7 +49,7 @@ from electrum.util import (UserCancelled, print_error,
                            WalletFileException, BitcoinException)
 # from electrum.wallet import Abstract_Wallet
 
-from .installwizard import InstallWizard, GoBack
+from .installwizard import InstallWizard
 
 
 try:

gui/qt/installwizard.py

@@ -10,7 +10,7 @@ from PyQt5.QtWidgets import *
 
 from electrum import Wallet, WalletStorage
 from electrum.util import UserCancelled, InvalidPassword
-from electrum.base_wizard import BaseWizard, HWD_SETUP_DECRYPT_WALLET
+from electrum.base_wizard import BaseWizard, HWD_SETUP_DECRYPT_WALLET, GoBack
 from electrum.i18n import _
 
 from .seed_dialog import SeedLayout, KeysLayout
@@ -19,10 +19,6 @@ from .util import *
 from .password_dialog import PasswordLayout, PasswordLayoutForHW, PW_NEW
 
 
-class GoBack(Exception):
-    pass
-
-
 MSG_ENTER_PASSWORD = _("Choose a password to encrypt your wallet keys.") + '\n'\
                      + _("Leave this field empty if you want to disable encryption.")
 MSG_HW_STORAGE_ENCRYPTION = _("Set wallet file encryption.") + '\n'\