Use safe event wrappers in signal handler signatures
Use safe event wrappers in signal handler signatures

The wrappers don't have any safe getters yet but they implement `AsRef`
for the respective FFI structs so all the event fields remain available
via `as_ref()`.

[breaking change]

EPashkin/rust-gnome-gtk,daa84/gtk,gkoz/rust-gnome-gtk,EPashkin/rust-gnome-gtk,gkoz/gtk-rs-gtk,rust-gnome/gtk,daa84/gtk,Susurrus/gtk,rust-gnome/gtk,gkoz/rust-gnome-gtk,gkoz/gtk-rs-gtk,Susurrus/gtk