Fix build against Weston 1.6 IVI Shell

Fix build against Weston 1.6 IVI Shell

Contains the following changes:

- Header inclusion statements for IVI Shell are updated:
  * ivi-layout.h has been removed upstream.
  * ivi-layout-export.h is used where private functions are not
    not needed, and ivi-layout-private.h is used where private
    functionality is needed.
- Extern has been added for ivi_layout_interface.
- A lot of IVI Shell functions have been un-camelcased as
  upstream has changed the naming convention.
- API usage has been updated to match upstream IVI Shell:
  * ivi_layout_get_properties_of_surface now returns the prop
    and the prop is now const.
  * ico_ivi_surfacePropertyNotification callback signature's prop
    is now const.
  * surface width and height are now updated to int32_t.
  * ivi_layout_surface_set_{position,dimension} now take in two
    integers instead of an array of two integers.
  * ivi_layout_surface_remove_notification and
    ivi_layout_surface_remove now return void.

Change-Id: I53c189539dc53edbf694f8cf37785fe834a8da84