ivi-shell: call shell_surface_send_configure() directly

For some reason, it seems that ivi-layout.c has tried hard to avoid
calling directly into ivi-shell.c. This means there is a jump through
hoops just to get the configure event sent to the clients. Ivi-shell
registers a listener for a ivi-layout signal for sending the event.

Instead, let ivi-layout.c call directly into ivi-shell.c, and expose a
function to send out the configure events. This reduces some confusion
on who calls what.

The main idea though is that this makes ivi-shell.c not depend on struct
ivi_layout_surface fields directly anymore. In following patches,
ivi_layout_surface can be made opaque for ivi-shell.c.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Emre Ucan <eucan@de.adit-jv.com>