Ability to set a layergroup as root layer

This improvement suggestion wants to solve 2 issues which are less optimal

• In WMS capabilities the service title is repeated as title of the service and as title of the root layer, in common WMS clients both levels are displayed, having the same title

• There is no option to sort the layers in a WMS capabilities root layer, if a wms client adds all layers at once, the layers are added alphabetically, and not as desired, eg polygon, line, point

If we allow to set a layergroup as rootlayer, layers in that group can be sorted and the rootlayer will have a proper title

requirements:

• only 1 layergroup can be set as rootlayer

• other layergroups should be of type container-tree, named-tree

• layers not in any group are not displayed in capabilities