[applets/taskmanager] Make the hover state clarifying, but not main

Summary:
I'm trying to make a custom appearance of the Task Manager by creating a new theme, but I ran into some issue. I expected that there are three main states (minimized, normal and active) and one clarifying state (hover). But I was surprised to find that there are four main states (minimized, normal, active and hover), and the hover state is also main, but not clarifying. I believe that the hover state should be clarifying for the main states, i.e. there must be three main states (minimized, normal and active) and three additional (minimzed-hover, normal-hover, active-hover).

BUG: 418318

See https://phabricator.kde.org/P555

Reviewers: davidedmundson, VDG

Reviewed By: davidedmundson

Subscribers: broulik, ngraham, epopov, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D28306