Fix systray tooltip's broken rich text track title
Changing (KStatusNotifier's) ToolTipTitle to 'Now playing' and the rich text track details to ToolTipSubTitle instead. According to https://techbase.kde.org/Development/Tutorials/PortToKStatusNotifierItem , "A KSNI tooltip is made of an icon, a title and a subtitle (which may contain some limited markup)."
Before: EngineController::prettyNowPlaying (containing markup tags) is set as tooltip title, and is not shown correctly. (attached image) After: EngineController::prettyNowPlaying is prepended to the tooltip subtitle, where it is displayed correctly, and "Now playing" (an existing translated string) set as tooltip title.
(Trying to figure out how Gitlab works, hope I'm doing it right(TM))