Add built-in OpenLayers map viewer

[dmorissette]

Every once in a while we get requests for a simple way to test a mapfile. One way to handle this could be to do as GeoServer does and provide a built-in OpenLayers based map viewer. In the GeoServer case, this viewer is returned when one issues a WMS GetMap request with format=application/openlayers in it.

I propose that we provide a similar functionality in MapServer, which would be triggered in one of two ways:

1- Using mapserv?map=/path/to/my.map&mode=openlayers ... in this case the viewer would be initialized based on the mapfile defaults, and some of the traditional mapserv CGI params may also work (such as map size, layer selection, etc.)

2- Using format=application/openlayers in a WMS GetMap request as GeoServer does. Note that in this case the rest of the GetMap parameters would be used to configure the map to view (BBOX, WIDTH, HEIGHT, LAYERS, etc.)

Both cases would call the same function internally to produce a simple OpenLayeres viewer with one singletile layer for the whole map with the selected layers.