Allow query operations (Identify,etc) on ags mapsources by using query-as

[brentfraser]

Addresses #747 by allowing ags layer query-as to reference an ags-vector layer :

    <map-source name="ags-polygons"               type="ags">
        <url>https://gis2.co.dakota.mn.us/arcgis/rest/services/DCGIS_OL_Transportation/MapServer/export</url>
        <layer name="runways" query-as="ags-polygons-query/runways">
            <param name="layers" value="show:21" />
        </layer>
    </map-source>
    <map-source name="ags-polygons-query"         type="ags-vector">
        <url>https://gis2.co.dakota.mn.us/arcgis/rest/services/DCGIS_OL_Transportation/MapServer/21</url>
        <layer name="runways"  title="Runways" >
            <template name="identify" auto="true" />
            <template name="select" alias="search"/>
        </layer>
    </map-source>

[theduckylittle]

I had to do manual surgery to get the one in... but it's done.