Basedata - add option to attach current ranges as the range property, same for sample counts

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Basedata objects have their ranges and sample counts implicitly calculated from 
the groups.  However, the user can also specify these properties at import, 
allowing one to, for example, use a subset of the geographic range when 
calculating endemism metrics.  

These can be specified when the data are imported, or when label properties are 
loaded. 

The issue is that it is a more involved process than it needs to be.  It should 
be possible to add them from the current basedata instance.  

The advantage of this approach is that the user can then run exclusions to 
delete groups from the basedata, retaining the original ranges and ample 
counts.  

Original issue reported on code.google.com by shawnlaffan on 31 Oct 2013 at 4:21