Allow configurable legend options in catalog files

[stevage]

Sometimes it'd be nice to override properties of a legend from a catalog file. Maybe something like:

{
              "url": "http://services.ga.gov.au/gis/rest/services/NEXIS_Residential_Population_Density/MapServer",
              "type": "esri-mapServer",
              "legendOptions": {
                "title":"People per cell"
              }
}

The options would just be passed directly through to the Legend object, no need to invent anything new here.

[RacingTadpole]

I think this is fixed by the "name" option in "tableStyle.columns", from #1302.