Make Appearance KCM tooltip texts consistent
Summary: Improve wording and add an ellipsis where needed in tooltips in Appearance KCMs.
Test Plan: Open for example the Plasma Theme KCM and hover over the "Edit Theme..." button.
Reviewers: Plasma, VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: VDG, plasma-devel, Plasma
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D19038