outdated wiki information

In the wiki, e.g. https://github.com/G-Node/nix/wiki/Model-Definition, an old version of the odML library is depicted, that still features `value` objects.

Open the wiki page Model-Definition linked in the issue and inspect the section describing odML. Compare its depiction with the current odML library model, then update the outdated information about value objects. Done means the wiki no longer presents the old version.

Written by the indexing model from the issue text.