wayland: added notification prototype, be more explicit about struct types

wayland: added notification prototype, be more explicit about struct types

Notification support can be implemented on genivi objects using the
genivi::notify::notifier, it is supposed to be inherited from by the
notification-needing types, e.g. genivi::surface.

Currently no implementation for notifier is present (only an empty
shell) also it is not yet clear, if the notifications will be sent from
the genivi objects method's or e.g. their thunks (which would simplify
the methods considerably).

Added request wrappers for genivi::surface and genivi::layer, just
inline them into the class and be done with it.

Signed-off-by: Marcus Fritzsch <marcus_fritzsch@mentor.com>