Update map.csv and document

I have updated map.csv again.  I also added documentation on the process I use.  

In addition I have modified the query that generates the employer table to use outer joins so that if some entity is not in the mapping table it will still be included in the aggregations.
I don't think so.  The table doesn't have a column called "type".

> On Sep 9, 2014, at 8:23 PM, Tom Dooner <notifications@github.com> wrote:
> 
> In assets/js/views/_categoryView.js:
> 
> >      _.each(this.collection, function( c ){
> > -      data.addRow([c.attributes.contype, c.attributes.amount]);
> > +      if (c.attributes.contype === 'Individual')
> I think you want "type" instead of "contype" here?
> 
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