Bugfix/data object management

[essweine]

This PR removes a terrible hack that implements data object inheritance. Rather than trying to make the workflow data all point to the same place, this stores data objects on the spec where they are created and checks successively higher levels until one is found and sets or gets a value there. It also introduces a data_objects key in the workflow data, which distinguishes data object values from other stuff that might be written to the workflow data.