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

Subscribers: plasma-devel

Tags: Plasma

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