Constructor
new SmartWMS()
Extension to the standard Leaflet WMS layer to add the ability for the layer class to lookup the bounding box from the WMS server, and to construct a polygon geoJSON object, with the pid of the layer in the properties object.
For this to work, the options object passed to the initialise method must include a property called wmsFeatureUrl, which contains the FULL url to lookup the features of the associated pid.