Port launch feedback KCM to Qt Quick and implement VDG redesign

Summary:
* Implements VDG mockup M112/364
** But using "Task Manager" naming for consistency instead of "Taskbar"
** Additional UI tweak of using i18np for spinbox suffices
* Switched from generic name "launch" to "launchfeedback"
** This will require i18n pot and doc HTML renames to match
* Original business logic is preserved as-is, but code is simplified and cleaned-up (coding style, etc.)

Depends on D8641.

Reviewers: #plasma, mart, abetts

Reviewed By: #plasma, mart

Subscribers: anthonyfieroni, mmustac, ngraham, davidedmundson, broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D8911