Use public WMS servers in map viewer configuration in geonetwork war distribution

[josegar74]

Actual war distribution use for map viewer the layers provided in geoserver.

As no geoserver.war with these custom layers is provided to download, the geonetwork maps doesn't show any layer (in war distribution) unless a manual configuration of layers in config-gui.xml is done.

I think is better for the geonetwork.war to provide the config-gui.xml file using a public WMS server for the maps, avoiding the need of manual configuration by the user.

For installer, as geoserver is also distributed we can keep actual configuration using geoserver layers.