update diagram accordingly

Signed-off-by: Mattias Andrée <maandree@operamail.com>
containers can not contain other containers (unless you make a new class and override this), this also implies that items cannot contain themself and vanish into the void

Signed-off-by: Mattias Andrée <maandree@operamail.com>
support for custom events

Signed-off-by: Mattias Andrée <maandree@operamail.com>
move class_inheritance into protected from public

Signed-off-by: Mattias Andrée <maandree@operamail.com>