D29511: Label: Add ping-pong logic

[Carson Black]

cblack added reviewers: Plasma, VDG.

REPOSITORY
  R242 Plasma Framework (Library)

REVISION DETAIL
  https://phabricator.kde.org/D29511

To: patrickelectric, #plasma, #vdg
Cc: kde-frameworks-devel, LeGast00n, cblack, michaelh, ngraham, bruns