Added ensurance that the selected style for a layer in a layer group is respected and not always using the default style of the layer
Fixed bug where layer groups with non default styles would always get default styles
Merge branch 'fix_wms_post_layergroup_styles' of https://github.com/koordo/geoserver into fix_wms_post_layergroup_styles
Refactored the layer style check into a helper method for readability