2fa wallet creation is broken on master

[ecdsa]

this is a regression caused by 4a37668

Traceback (most recent call last):
  File "/opt/electrum/electrum/gui/qt/wizard/wizard.py", line 237, in on_next_button_clicked
    raise e
  File "/opt/electrum/electrum/gui/qt/wizard/wizard.py", line 233, in on_next_button_clicked
    self.load_next_component(view.view, view.wizard_data, view.params)
  File "/opt/electrum/electrum/gui/qt/wizard/wizard.py", line 157, in load_next_component
    page.on_ready()  # call before component emits any signals
  File "/opt/electrum/electrum/plugins/trustedcoin/qt.py", line 484, in on_ready
    self.wizard.trustedcoin_qhelper.createKeystore()
  File "/opt/electrum/electrum/plugins/trustedcoin/common_qt.py", line 133, in createKeystore
    xprv1, xpub1, xprv2, xpub2, xpub3, short_id = self.plugin.create_keys(wizard_data)
  File "/opt/electrum/electrum/plugins/trustedcoin/trustedcoin.py", line 624, in create_keys
    xprv1, xpub1, xprv2, xpub2 = self.xkeys_from_seed(wizard_data['seed'], wizard_data['seed_extra_words'])
KeyError: 'seed_extra_words'