weston-ivi-shell: Remove child context of a layer when the main context of the layer is removed

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@denso.co.jp>
ilmControl and weston-ivi-shell: Reverse order when client is added to resources.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@denso.co.jp>