task-x11-illume: rename to packagegroup-x11-illume

* add RPROVIDES/RREPLACES/RCONFLICTS task-x11-illume for upgrade path
* RDEPEND on packagegroup-core-x11* from oe-core now with task-x11-*
  gone from meta-oe

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>