Fixed T24565 - Improved loading/reinit time

Summary:
Additionally improved const correctness of public
DataStorage interface a bit

Signed-off-by: Ralf Floca <r.floca@dkfz-heidelberg.de>

Added missing update in ArbitraryTimeGeometry::Initialize

Signed-off-by: Ralf Floca <r.floca@dkfz-heidelberg.de>

Test Plan: Unit tests

Reviewers: O1 MITK Core!

Maniphest Tasks: T24565

Differential Revision: https://phabricator.mitk.org/D117