Problems with `plot` module

[ashleyrback]

Some problems with the plot module:

• [ ] plot_projection bars are too wide, so you can't see any detail in the spectrum when plotted.
• [ ] plot_surface fails with the error below. This may be due to removing the Axes3D module that I thought was unused, in #76.

I'll investigate.

ValueError                                Traceback (most recent call last)
<ipython-input-13-3378db744f5a> in <module>()
----> 1 plot.plot_surface(spectrum_1, "energy_mc", "radial_mc")

/home/ashley/snoplus/software/echidna/echidna/echidna/output/plot.pyc in plot_surface(spectra, dimension1, dimension2)
    192     """
    193     fig = plt.figure()
--> 194     axis = fig.add_subplot(111, projection='3d')
    195     index1 = spectra.get_config().get_index(dimension1)
    196     index2 = spectra.get_config().get_index(dimension2)

/usr/lib/pymodules/python2.7/matplotlib/figure.pyc in add_subplot(self, *args, **kwargs)
    894         else:
    895             projection_class, kwargs, key = process_projection_requirements(
--> 896                 self, *args, **kwargs)
    897 
    898             # try to find the axes with this key in the stack

/usr/lib/pymodules/python2.7/matplotlib/projections/__init__.pyc in process_projection_requirements(figure, *args, **kwargs)
    117 
    118     if isinstance(projection, basestring) or projection is None:
--> 119         projection_class = get_projection_class(projection)
    120     elif hasattr(projection, '_as_mpl_axes'):
    121         projection_class, extra_kwargs = projection._as_mpl_axes()

/usr/lib/pymodules/python2.7/matplotlib/projections/__init__.pyc in get_projection_class(projection)
     61         return projection_registry.get_projection_class(projection)
     62     except KeyError:
---> 63         raise ValueError("Unknown projection '%s'" % projection)
     64 
     65 

ValueError: Unknown projection '3d'