Plotting functions fail for multi trajectory results

[BryanRumsey]

result.plot_property('type') fails when number_of_trajectories > 1

Error from StochSS

[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'