[PD] make pointers to the UI std::unique_ptr

Same as PR #4293, just for PartDesign

as noted in https://github.com/FreeCAD/FreeCAD/pull/4271#discussion_r554673632
the pointer to the UI should be a unique pointer.

This PR does this for all PartDesign dialogs that don't already use a unique_ptr.

src/Mod/PartDesign/Gui/TaskFilletParameters.cpp

@@ -54,10 +54,10 @@ using namespace Gui;
 
 TaskFilletParameters::TaskFilletParameters(ViewProviderDressUp *DressUpView, QWidget *parent)
     : TaskDressUpParameters(DressUpView, true, true, parent)
+    , ui(new Ui_TaskFilletParameters)
 {
     // we need a separate container widget to add all controls to
     proxy = new QWidget(this);
-    ui = new Ui_TaskFilletParameters();
     ui->setupUi(proxy);
 
     this->groupLayout()->addWidget(proxy);
@@ -214,8 +214,6 @@ TaskFilletParameters::~TaskFilletParameters()
 {
     Gui::Selection().clearSelection(); 
     Gui::Selection().rmvSelectionGate();
-
-    delete ui;
 }
 
 bool TaskFilletParameters::event(QEvent *e)