added surface content observer to ivi-layout

this is used by other weston modules, that are interested in
content state of surfaces.

Signed-off-by: Timo Lotterbach <timo.lotterbach@bmw-carit.de>
Fix seg-fault during a test-application running.
Transition animation support when attribute change of surface happens by ivi-layout api.

interpolate frames during transition.

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