Surface: new Extend icon for existing Surface_ExtendFace command

The icon is added to the `.qrc` resource file.

The command is added to the Surface toolbar.

src/Mod/Surface/Gui/Command.cpp

@@ -232,6 +232,7 @@ CmdSurfaceExtendFace::CmdSurfaceExtendFace()
     sToolTipText  = QT_TR_NOOP("Extend face");
     sWhatsThis    = "Surface_ExtendFace";
     sStatusTip    = sToolTipText;
+    sPixmap       = "Surface_Extend";
 }
 
 void CmdSurfaceExtendFace::activated(int)

src/Mod/Surface/Gui/Resources/Surface.qrc

@@ -3,6 +3,7 @@
         <file>icons/Surface_BezierSurface.svg</file>
         <file>icons/Surface_BSplineSurface.svg</file>
         <file>icons/Surface_Cut.svg</file>
+        <file>icons/Surface_Extend.svg</file>
         <file>icons/Surface_Filling.svg</file>
         <file>icons/Surface_Sections.svg</file>
         <file>icons/Surface_Sewing.svg</file>

src/Mod/Surface/Gui/Workbench.cpp

@@ -71,7 +71,8 @@ Gui::ToolBarItem* Workbench::setupToolBars() const
     surface->setCommand( "Surface" );
     *surface << "Surface_Filling"
              << "Surface_GeomFillSurface"
-             << "Surface_Sections";
+             << "Surface_Sections"
+             << "Surface_ExtendFace";
 /*  *surface << "Surface_Cut"; */
 
     return root;