D20536: Use consistent default Kickoff user icon

[Björn Feber]

GB_2 added a dependency: D20564: Change default user avatar.

REPOSITORY
  R266 Breeze Icons

REVISION DETAIL
  https://phabricator.kde.org/D20536

To: GB_2, #plasma, #vdg
Cc: ngraham, #vdg, kde-frameworks-devel, #plasma, michaelh, bruns