Make `visualize` subcommand compatible with jupyter notebook

[sean-la]

Running the PATHOGIST visualize in a jupyter notebook with a BASH kernel doesn't work.
We get the following error:

07:48:03 AM (3427 ms) -> INFO:Visualing clusterings...
Traceback (most recent call last):
  File "/home/klw17/dev/PathOGiST/PATHOGIST", line 319, in <module>
    main()
  File "/home/klw17/dev/PathOGiST/PATHOGIST", line 316, in main
    visualize(param)
  File "/home/klw17/dev/PathOGiST/PATHOGIST", line 227, in visualize
    pathogist.visualize.visualize_clusterings(summary_clustering)
  File "/home/klw17/dev/PathOGiST/pathogist/visualize.py", line 111, in visualize_clusterings
    ax = plt.subplot(num_rows,num_cols,subplot_index)
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/site-packages/matplotlib/pyplot.py", line 1071, in subplot
    fig = gcf()
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/site-packages/matplotlib/pyplot.py", line 601, in gcf
    return figure()
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/site-packages/matplotlib/pyplot.py", line 548, in figure
    **kwargs)
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/site-packages/matplotlib/backend_bases.py", line 161, in new_figure_manager
    return cls.new_figure_manager_given_figure(num, fig)
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/site-packages/matplotlib/backends/_backend_tk.py", line 1044, in new_figure_manager_given_figure
    window = Tk.Tk(className="matplotlib")
  File "/home/klw17/anaconda3/envs/pathogist2/lib/python3.5/tkinter/__init__.py", line 1876, in __init__
    self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)
_tkinter.TclError: no display name and no $DISPLAY environment variable
(pathogist2)