Plasma uses inconsistent terminology to refer to KRunner, calling it "Run Command" in
Kicker/Kickoff/etc, but "Plasma Search" in System Settings. For reasons explained in
T10966: Unify how we refer to KRunner neither term is ideal, and the inconsistency is bad too.
This patch unifies on "Show KRunner" for the action and "KRunner" for the KCM name,
transforming it into a recognizable brand name like Apple's Spotlight.
This patch also makes the icons consistent and adjusts some strings to more clearly
indicate what KRunner is and does.