0028985: XCAF data structures for generic text annotations linked to GD&T annotations and saved views

1. A tool to annotate items in the hierarchical product structure was added. The tool is located under
   fixed label 0:1:9. It operates two basic entities: notes and annotations located under 0:1:9:1 and 0:1:9:2
   hives correspondingly. A note is an attribute derived from base class XCAFDoc_Note that is attached to a separate
   label under the notes hive. An annotated item is represented by XCAFDoc_AssemblyItemRef attribute
   attached to a separate label under the annotated items hive. Notes are linked to annotated items by means of
   XCAFDoc_GraphNode attribute, where notes play parent roles and annotated items - child roles.
2. XCAFDoc_AssemblyItemRef defines a weak reference to a label with optional attribute GUID or sub-shape index.
3. A capability to store note/annotation labels in XCAFDoc_ViewTool was added.
4. XDE User guide was updated

src/XCAFDoc/XCAFDoc_NoteComment.hxx

@@ -0,0 +1,72 @@
+// Created on: 2017-02-13
+// Created by: Sergey NIKONOV
+// Copyright (c) 2000-2017 OPEN CASCADE SAS
+//
+// This file is part of Open CASCADE Technology software library.
+//
+// This library is free software; you can redistribute it and/or modify it under
+// the terms of the GNU Lesser General Public License version 2.1 as published
+// by the Free Software Foundation, with special exception defined in the file
+// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
+// distribution for complete text of the license and disclaimer of any warranty.
+//
+// Alternatively, this file may be used under the terms of Open CASCADE
+// commercial license or contractual agreement.
+
+#ifndef _XCAFDoc_NoteComment_HeaderFile
+#define _XCAFDoc_NoteComment_HeaderFile
+
+#include <XCAFDoc_Note.hxx>
+
+class XCAFDoc_NoteComment;
+DEFINE_STANDARD_HANDLE(XCAFDoc_NoteComment, XCAFDoc_Note)
+
+//! A comment note attribute.
+//! Contains a textual comment.
+class XCAFDoc_NoteComment : public XCAFDoc_Note
+{
+public:
+
+  DEFINE_STANDARD_RTTIEXT(XCAFDoc_NoteComment, XCAFDoc_Note)
+
+  Standard_EXPORT static const Standard_GUID& GetID();
+
+  //! Finds a reference attribute on the given label and returns it, if it is found
+  Standard_EXPORT static Handle(XCAFDoc_NoteComment) Get(const TDF_Label& theLabel);
+
+  //! Create (if not exist) a comment note on the given label.
+  //! \param [in] theLabel     - note label.
+  //! \param [in] theUserName  - the name of the user, who created the note.
+  //! \param [in] theTimeStamp - creation timestamp of the note.
+  //! \param [in] theComment   - comment text.
+  Standard_EXPORT static Handle(XCAFDoc_NoteComment) Set(const TDF_Label&                  theLabel,
+                                                         const TCollection_ExtendedString& theUserName,
+                                                         const TCollection_ExtendedString& theTimeStamp,
+                                                         const TCollection_ExtendedString& theComment);
+
+  //! Creates an empty comment note.
+  Standard_EXPORT XCAFDoc_NoteComment();
+
+  //! Sets the comment text.
+  Standard_EXPORT void Set(const TCollection_ExtendedString& theComment);
+
+  //! Returns the comment text.
+  Standard_EXPORT const TCollection_ExtendedString& Comment() const;
+
+public:
+
+  // Overrides TDF_Attribute virtuals
+  Standard_EXPORT const Standard_GUID& ID() const Standard_OVERRIDE;
+  Standard_EXPORT Handle(TDF_Attribute) NewEmpty() const Standard_OVERRIDE;
+  Standard_EXPORT void Restore(const Handle(TDF_Attribute)& theAttrFrom) Standard_OVERRIDE;
+  Standard_EXPORT void Paste(const Handle(TDF_Attribute)&       theAttrInto,
+                             const Handle(TDF_RelocationTable)& theRT) const Standard_OVERRIDE;
+  Standard_EXPORT Standard_OStream& Dump(Standard_OStream& theOS) const Standard_OVERRIDE;
+
+protected:
+
+  TCollection_ExtendedString myComment; ///< Comment text.
+
+};
+
+#endif // _XCAFDoc_NoteComment_HeaderFile