Fixed WmscRequest query string

[JBou]

This PR fixes the appending of the query string.

I wanted to use this service in MapsUi: https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows

When using it like above, the query string got added like this:
https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows&SERVICE=WMS&REQUEST=GetMap&BBOX=... wich resulted in an error 404.

I then added ?REQUEST=GetCapabilities to my service url:
https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows?REQUEST=GetCapabilities
which created this url: /geoserver/p_bz-Cadastre/ows?REQUEST=GetCapabilities&SERVICE=WMS&REQUEST=GetMap&BBOX=
and this error:

<?xml version="1.0" encoding="UTF-8"?>
<ows:ExceptionReport xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:ows="http://www.opengis.net/ows" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="1.0.0" xsi:schemaLocation="http://www.opengis.net/ows https://geoservices5.civis.bz.it/geoserver/schemas/ows/1.0.0/owsExceptionReport.xsd">
	<ows:Exception exceptionCode="InvalidParameterValue" locator="request">
		<ows:ExceptionText>Single value expected for request parameter request but instead found: [GetCapabilities, GetMap]</ows:ExceptionText>
	</ows:Exception>
</ows:ExceptionReport>

There are 2 workarounds:

• Add request as lowercase string as in the wms sample
  https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows?request=GetCapabilities
  In this case there is still a REQUEST=GetMap added and the lowercase request makes some confusion.

• Add any dummy parameter
  https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows?dummy

With this PR you can use the url without query parameters as source (e.g. https://geoservices5.civis.bz.it/geoserver/p_bz-Cadastre/ows) which makes it more obvious.

We could further improve it to completely replace the existing query parameters. I already prepared a solution, can push it if you decide to go this way (it uses an utility class named QueryString):

            var url = new UriBuilder(_baseUrl.AbsoluteUri);
            var query = new QueryString();

            query.Set("SERVICE", "WMS");
            if (!string.IsNullOrEmpty(_version)) query.Set("VERSION", _version);
            query.Set("REQUEST", "GetMap");
            query.Set("BBOX", TileTransform.TileToWorld(new TileRange(info.Index.Col, info.Index.Row), info.Index.Level, _schema).ToString());
            query.Set("FORMAT", _schema.Format);
            query.Set("WIDTH", _schema.GetTileWidth(info.Index.Level).ToString());
            query.Set("HEIGHT", _schema.GetTileHeight(info.Index.Level).ToString());
            var crsParameterName = !string.IsNullOrEmpty(_version) && string.CompareOrdinal(_version, "1.3.0") >= 0 ? "CRS" : "SRS";
            query.Set(crsParameterName, _schema.Srs);
            query.Set("LAYERS", ToCommaSeparatedValues(_layers));
            if (_styles != null && _styles.Count > 0) query.Set("STYLES", ToCommaSeparatedValues(_styles));
            AppendCustomParameters(query);
            url.Query = query.ToString();
            return new Uri(url.ToString());

[JBou]

I was on an old source code, I saw that you updated to netstandard2.0 in the meantime.
in that case we can use HttpUtility.ParseQueryString() instead of the QueryString class.

[pauldendulk]

I was on an old source code, I saw that you updated to netstandard2.0 in the meantime. in that case we can use HttpUtility.ParseQueryString() instead of the QueryString class.

Is this something you want to add as part of this PR?