[Doc] Improve topics within App

- The location of the documentation is improved (not in the cpp file
  anymore but in core-app.dox).  This prevents cluttering source with
  high-level overviews typical of topic documentation.
- The formatting has been made consistent.

src/App/PropertyContainer.cpp

@@ -640,50 +640,3 @@ void PropertyData::visitProperties(OffsetBase offsetBase,
     };
 }
 
-/** \defgroup PropFrame Property framework
-    \ingroup APP
-    \brief System to access object properties
-\section propframe_intro Introduction
-The property framework introduces the ability to access attributes (member variables) of a class by name without
-knowing the class type. It's like the reflection mechanism of Java or C#.
-This ability is introduced by the App::PropertyContainer class and can be used by all derived classes.
-
-This makes it possible in the first place to make an automatic mapping to python (e.g. in App::FeaturePy) and
-abstract editing properties in Gui::PropertyEditor.
-
-\section Examples
-
-Here some little examples how to use it:
-
-\code
-// search in PropertyList
-Property *prop = _pcFeature->getPropertyByName(attr);
-if(prop)
-{
-  return prop->getPyObject();
-}
-\endcode
-
-or:
-
-\code
-void PropertyContainer::Restore(Base::Reader &reader)
-{
-  reader.readElement("Properties");
-  int Cnt = reader.getAttributeAsInteger("Count");
-
-  for(int i=0 ;i<Cnt ;i++)
-  {
-    reader.readElement("Property");
-    string PropName = reader.getAttribute("name");
-    Property* prop = getPropertyByName(PropName.c_str());
-    if(prop)
-      prop->Restore(reader);
-
-    reader.readEndElement("Property");
-  }
-  reader.readEndElement("Properties");
-}
-\endcode
-
-*/