[openpgp] i18n helper don't imported

Versions

• OS: Linux
• GTK+ Version: 3.22.30
• PyGObject Version: 3.26.1
• python-nbxmpp Version: 0.6.8
• Gajim Version: 1.0.99.1

Traceback

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gajim/chat_control_base.py", line 434, in change_encryption
    if not plugin.activate_encryption(self):
  File "/home/orhideous/.local/share/gajim/plugins/openpgp/pgpplugin.py", line 156, in activate_encryption
    from openpgp.gtk.wizard import KeyWizard
  File "/home/orhideous/.local/share/gajim/plugins/openpgp/gtk/wizard.py", line 107, in <module>
    class WelcomePage(Gtk.Box):
  File "/home/orhideous/.local/share/gajim/plugins/openpgp/gtk/wizard.py", line 110, in WelcomePage
    title = _('Welcome')
NameError: name '_' is not defined

Steps to reproduce the problem

1. Download and activate OpenPGP plugin
2. Try to switch encryption mode from PGP to OpenPGP
3. KABOOM!