Cleanup of surface management in Sources (centralize texturesurface_ in

Source class, avoid mistakes in subclasses). Integration of sources in
AppearanceView (not functionnal yet).

StreamSource.h

@@ -39,7 +39,6 @@ public:
 
 protected:
     void init() override;
-    void replaceRenderingShader() override;
 
     Stream *stream_;
 };