Generalize multi-index access

Implement resolveDynamicMultiIndex() and resolveStaticMultiIndex(). While the latter simply chains [i] calls for all entries i of the multi-index the former has to be given a termination criterion. For the static version we require, that the containers operator[] supports the multi-index entries directly. For a nested multi-type container, you can e.g. use a corresponding HybridTreePath as multi-index.

In principle resolveDynamicMultiIndex superceeds hybridIndexAccess() but the interface is slightly different. However, habridIndexAccess() may be deprecated at a later stage.