ENYO-2431: Updated layout.design to remove unused "isContainer" properties

Enyo-DCO-1.1-Signed-off-by: Yves Del Medico <yves.del-medico@hp.com>
ENYO-2431: Updated layout.design to fix or remove "content" properties

Enyo-DCO-1.1-Signed-off-by: Yves Del Medico <yves.del-medico@hp.com>