Properly scale link overlays

src/Gui/Icons/LinkOverlay.xpm

@@ -1,13 +0,0 @@
-/* XPM */
-const char *xpm_link[] = {
-"6 6 3 1",
-"  c None",
-"# c #000000",
-"a c #ffffff",
-"######",
-"aaaaa#",
-"##aaa#",
-"#aa#a#",
-"aa##a#",
-"##..##"};
-

src/Gui/Icons/resource.qrc

@@ -270,7 +270,6 @@
         <file>LinkArrayOverlay.svg</file>
         <file>LinkSubOverlay.svg</file>
         <file>LinkSubElement.svg</file>
-        <file>LinkOverlay.xpm</file>
         <file>LinkArrayOverlay.xpm</file>
         <file>LinkSubOverlay.xpm</file>
         <file>LinkSubElement.xpm</file>

src/Gui/Tree.cpp

@@ -5417,9 +5417,10 @@ void DocumentObjectItem::testStatus(bool resetStatus, QIcon& icon1, QIcon& icon2
 
         if (currentStatus & Status::External) {
             static QPixmap pxExternal;
+            int px = 12 * getMainWindow()->devicePixelRatioF();
             if (pxExternal.isNull()) {
                 pxExternal = Gui::BitmapFactory().pixmapFromSvg("LinkOverlay",
-                                                              QSize(24, 24));
+                                                              QSize(px, px));
             }
             pxOff = BitmapFactory().merge(pxOff, pxExternal, BitmapFactoryInst::BottomRight);
             pxOn = BitmapFactory().merge(pxOn, pxExternal, BitmapFactoryInst::BottomRight);