Move legend in DVH to more appropriate position

[GoogleCodeExporter]

Currently the DVH legend blocks plot lines in the top right hand corner. 
Ideally the legend should be moved so it does not block any of the plot. This 
probably can be found by investigating the matplotlib library documentation 
found at http://matplotlib.org

Another option is to disable the legend completely and use the structure 
selector on the left as a legend.

Original issue reported on code.google.com by bastula on 3 Oct 2012 at 3:30

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[roycoding]

This may require a newer version of matplotlib, but it is definitely possible to move the legend outside the plot box: http://matplotlib.org/users/legend_guide.html#legend-location