Bug in plot2d stack demo

[ericdill]

/home/edill/anaconda/envs/nikea/bin/python /home/edill/dev/python/bubblegum/qt_apps/pyqt/DEMO_plot2Dstack.py
Traceback (most recent call last):
  File "/home/edill/dev/python/bubblegum/qt_apps/pyqt/DEMO_plot2Dstack.py", line 104, in <module>
    tt = StackExplorer()
  File "/home/edill/dev/python/bubblegum/qt_apps/pyqt/DEMO_plot2Dstack.py", line 98, in __init__
    key_list=key_list)
  File "/home/edill/dev/python/bubblegum/bubblegum/qt_widgets/__init__.py", line 58, in __init__
    key_list=key_list)
  File "/home/edill/dev/python/bubblegum/bubblegum/messenger/mpl/cross_section_2d.py", line 67, in __init__
    self._view = CrossSection2DView(fig=self._fig, data_list=data_list,
AttributeError: 'CrossSection2DMessenger' object has no attribute '_fig'

Process finished with exit code 1