Big update to remove deprecation warning from Qt 5.15.0

That is need on MacOS build as travis log is bigger than 50k lines
which breaks travis rules
And by the way deprecations are real
All file contains the same modification replace 0 to Qt::WindowFlags() when needed
as the class needs to be instantiated

Signed-off-by: vejmarie <jmverdun3@gmail.com>

src/Mod/MeshPart/Gui/CrossSections.h

@@ -44,7 +44,7 @@ class CrossSections : public QDialog
     enum Plane { XY, XZ, YZ };
 
 public:
-    CrossSections(const Base::BoundBox3d& bb, QWidget* parent = 0, Qt::WindowFlags fl = 0);
+    CrossSections(const Base::BoundBox3d& bb, QWidget* parent = 0, Qt::WindowFlags fl = Qt::WindowFlags());
     ~CrossSections();
     void accept();
     void apply();

src/Mod/MeshPart/Gui/Tessellation.h

@@ -47,7 +47,7 @@ class Mesh2ShapeGmsh : public MeshGui::GmshWidget
     Q_OBJECT
 
 public:
-    Mesh2ShapeGmsh(QWidget* parent = 0, Qt::WindowFlags fl = 0);
+    Mesh2ShapeGmsh(QWidget* parent = 0, Qt::WindowFlags fl = Qt::WindowFlags());
     ~Mesh2ShapeGmsh();
 
     void process(App::Document* doc, const std::list<App::SubObjectT>&);