The Big Cleanup of kde-workspace/plasma

- Plasma screensaver is dead, this needs a rewrite
- qmlpackages move into desktop, all code is desktop-specific at this
  point
- design subdir moves into desktop/, this section needs reviewing and
  updating entirely, for now, it's reasonable to assume it's desktop-only

This way, we end up with generic, and desktop-specific components, ready
for splitting up into separate repositories.

CCMAIL:plasma-devel@kde.org