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

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 TD dialogs that don't already use a unique_ptr.

src/Mod/TechDraw/Gui/TaskDetail.cpp

@@ -238,7 +238,6 @@ TaskDetail::TaskDetail(TechDraw::DrawViewDetail* detailFeat):
 TaskDetail::~TaskDetail()
 {
     m_ghost->deleteLater();  //this might not exist if scene is destroyed before TaskDetail is deleted?
-    delete ui;
 }
 
 void TaskDetail::updateTask()