Enable an application re-launch

When an application dies after requestSurface,
the application can't be launched because
Window Manager doesn't know the application is dead and doesn't
clean up its database.

In other case, when Mixer app dies due to pulse audio crash
just before Window Manager handles surface memory,
the connection between weston and Window Manager is dead.

So add following
* Add context setting with window manager clients.
  Terminate the context and clean up WM database
  if a client application is dead.
* Add layout_commit() after add surfaces to layer.

[PatchSet 2]
* Add layout_commit() after add surfaces to layer
  in api_request_surface

Bug-AGL: SPEC-1086

Change-Id: I6ecae2606ac644e49a3383ba849390f8c235f187
Signed-off-by: Kazumasa Mitsunari <knimitz@witz-inc.co.jp>