packagegroup: inherit packagegroup, drop PACKAGES and ALLOW_EMPTY

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Change-Id: I41bab57213c03cb5a4f2b5635fd7b15bcd660b1b
Reviewed-on: http://g2g.palm.com/1099
Reviewed-by: Susan Montooth <susan.montooth@palm.com>
Tested-by: Susan Montooth <susan.montooth@palm.com>