Use non deprecated fastInsert in baloo

Summary: Replace the deprecated uds insert method by fastInsert.

Reviewers: dfaure, Frameworks, broulik, Baloo, ngraham

Reviewed By: broulik, Baloo, ngraham

Subscribers: kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D15740