Unify inserting data between FileFetchJob and IndexedDataRetriever

Summary:
Unify how the data is updated between the different jobs.
Also fixes a case where editable data was added before
actually checking that editing is possible.

Reviewers: bruns, ngraham

Reviewed By: ngraham

Subscribers: #baloo

Tags: #baloo

Differential Revision: https://phabricator.kde.org/D23220