Better install wizard

Break out the workflow logic of the install wizard
into a base class.  This means reimplementing with
full support in a new GUI is now easy; you just provide
ways to request passwords, show messages etc.  The API
is fully documented in the base class.

There are a couple of minor outstanding issues, including that
the old messages shown when recovering a wallet are missing.
I will come back to that.  Ledger wallet might be broken.

Other improvements:

The install wizard code is now easy to follow and understand.
Hardware wallets can now be restored without any need for their
accompanying libraries.
Various bits of trustedcoin were broken and have been fixed.
Many plugin hooks can be removed.  I have only started on this.

plugins/trustedcoin/qt.py

@@ -18,6 +18,7 @@
 
 from functools import partial
 from threading import Thread
+import re
 
 from PyQt4.QtGui import *
 from PyQt4.QtCore import *
@@ -28,8 +29,9 @@ from electrum_gui.qt.amountedit import AmountEdit
 from electrum_gui.qt.main_window import StatusBarButton
 from electrum.i18n import _
 from electrum.plugins import hook
+from electrum import wizard
 
-from trustedcoin import TrustedCoinPlugin, Wallet_2fa
+from trustedcoin import TrustedCoinPlugin, Wallet_2fa, DISCLAIMER, server
 
 def need_server(wallet, tx):
     from electrum.account import BIP32_Account
@@ -90,6 +92,11 @@ class Plugin(TrustedCoinPlugin):
         return WaitingDialog(window, 'Getting billing information...', task,
                              on_finished)
 
+    def show_disclaimer(self, wallet, window):
+        icon = QPixmap(':icons/trustedcoin.png')
+        window.confirm('\n\n'.join(DISCLAIMER), icon=icon)
+        self.set_enabled(wallet, True)
+
     @hook
     def abort_send(self, window):
         wallet = window.wallet
@@ -225,10 +232,9 @@ class Plugin(TrustedCoinPlugin):
         email_e.setFocus(True)
 
         if not window.exec_():
-            return
+            raise wizard.UserCancelled
 
-        email = str(email_e.text())
-        return email
+        return str(email_e.text())
 
 
     def setup_google_auth(self, window, _id, otp_secret):