Ref T261, correct implementation of client provider

* made the interface a "real" interface and provided implementation as CCLientProvider
* aligned some function names with networl context
* network context "impl" also implements ICLientProvider

src/blackgui/models/clientlistmodel.h

@@ -29,7 +29,6 @@ namespace BlackGui
         //! Client list model
         class BLACKGUI_EXPORT CClientListModel : public CListModelBase<BlackMisc::Network::CClient, BlackMisc::Network::CClientList>
         {
-
         public:
             //! Constructor
             explicit CClientListModel(QObject *parent = nullptr);
@@ -39,7 +38,6 @@ namespace BlackGui
 
             //! \copydoc QAbstractListModel::data()
             virtual QVariant data(const QModelIndex &index, int role) const override;
-
         };
     } // namespace
 } // namespace