Draft: Patch Bug 519125 - Improve face tag query performance: CREATE INDEX idx_itp_tagid_property ON ImageTagProperties(tagid, property(50));

I've attempted on fixing https://bugs.kde.org/show_bug.cgi?id=519125

However, I lack the knowledge of the project and how things are done, and did not even succeed in building it.

So I think this will be of little use. Feel free to close this MR and let the implementation up to a pro :)