Add recipe notification read access.

[Luciole]

Currently we have write access to recipe notifications using PlayerLua.clear_recipe_notifications() and PlayerLua.add_recipe_notification(recipe).
But we can't know about current recipe notifications with something like PlayerLua.get_recipe_notifications().

Why:
To allow to synchronize recipe notifications status between maps for mods like Clusterio.

[Bilka]

Okay, added for 2.0.67.