Rethought the viewing/plotting framework a bit.  Namely:
- methods to actually render plots exist in plotting/renderers.py
- methods to show contained plots exist in plotting/double_plot.py and plotting/single_plot.py
- Generally, a class will be created in plotting/viewers.py for each data type.  Each class will know how to present data to the single_plot.py or double_plot.py.
- Deleted a lot of old plotting methods from hyperspy.  The rest of these will be used as guidelines for Chaco plots in the main framework.
- moved a k-means method to the mda/mda_sklearn.py file.  Needs to be refactored to not use MDP.