0024831: Make iterators of NCollection classes STL-compatible

STL-compatible iterators returned methods begin() and end() are provided in collection classes from NCollection package.
NCollection_Array1::Iterator is redesigned to use pointer instead of index.
Iterators of Sequence, Array, and Vector are extended by new methods to iterate backwards.

Use of SortTools_QuickSortOfReal is replaced by std::sort() in a few places (where possible).

src/NCollection/NCollection_Array2.hxx

@@ -40,7 +40,11 @@
 template <class TheItemType> class NCollection_Array2
   : public NCollection_BaseCollection<TheItemType>
 {
- public:
+public:
+  //! STL-compliant typedef for value type
+  typedef TheItemType value_type;
+
+public:
   // **************** Implementation of the Iterator interface.
   class Iterator : public NCollection_BaseCollection<TheItemType>::Iterator
   {