filenamesearch:/ define a title for the query

Summary: CCBUG: 420354

Reviewers: ngraham, elvisangelaccio, #dolphin, #frameworks, iasensio

Reviewed By: elvisangelaccio, #dolphin, iasensio

Subscribers: iasensio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D29198