Removed Snapshot import from observable addition by category (no affect on final combWS)

This MR affects how the final observables list in the combined workspace gets populated by category. It prevents the snapshot of observables (i.e. all/any objects on which the observable is dependent) from being imported into the final observables list. Doing so prevents a crash that occurs when creating the combined dataset if any observables are dependent on non-fundamental objects. All objects, fundamental and non-fundamental, observable or not, are still imported into the final combined workspace; now there are no non-fundamental objects trying to be imported into the combined dataset.