Add a proper kernel interface `INotifications` for the notifications component instead of using a C style interface.
Add parameter for the application name when initializing notifications to avoid hardcoding the application name.
The implementation for macOS is kept in Objective-C and a TODO is added, as the API we are currently using appears to be deprecated.
Add libnotify support for linux client
Also unify notification management
Make libnotify mandatory for the client. It is installed on 100% of Arch
Linux systems and on 70% of Debian systems. I'd guess the remaining
Debian systems are servers.
Detect dependent libraries of `libnotify` using `pkg-config`. Remove
library-specific code from the game module. Decrement refcount for
libnotify notification object before leaving the function.