Refactor NameIndexIterator into template class

Create template class GenericIndexIterator from NameIndexIterator.

NodeListener::NodeChanged(): Provide old value

* Add interface OldNodeAttributes an instance of which is passed to
NodeListener::NodeChanged() to provide the old attribute values
(currently only modification time and file size).
* Also extend PackageLinksListener::PackageLinkNodeChanged() with a
OldNodeAttributes parameter.
* Add OldNodeAttributes implementations for PackageLinkSymlink (inner
class OldAttributes) and UnpackingNode (OldUnpackageNodeAttributes).

Add NameIndex class and create instance in Volume

Refactor NameIndexIterator into template class

Create template class GenericIndexIterator from NameIndexIterator.

NodeListener::NodeChanged(): Provide old value

* Add interface OldNodeAttributes an instance of which is passed to
NodeListener::NodeChanged() to provide the old attribute values
(currently only modification time and file size).
* Also extend PackageLinksListener::PackageLinkNodeChanged() with a
OldNodeAttributes parameter.
* Add OldNodeAttributes implementations for PackageLinkSymlink (inner
class OldAttributes) and UnpackingNode (OldUnpackageNodeAttributes).

Add NameIndex class and create instance in Volume