Investigate spatial workflow result plotting

[BryanRumsey]

Single trajectory results display properly, however multi trajectory results produce the following error:

Error

[E 21:06:53 StochSS stochss_errors.py:56] Exception information: {'Reason': 'Uncaught Critical Error', 'Message': "'list' object has no attribute 'plot_property'"}
    Traceback (most recent call last):
      File "/stochss/stochss/handlers/workflows.py", line 256, in get
        fig = job.get_plot_from_spatial_results(
      File "/stochss/stochss/handlers/util/stochss_job.py", line 521, in get_plot_from_spatial_results
        fig = result.plot_property(
    AttributeError: 'list' object has no attribute 'plot_property'

[BryanRumsey]

This issue has a corresponding issue in SpatialPy #348