Extract keybinding handling to separate module

src/app/mod.rs

@@ -1,5 +1,6 @@
 pub mod app;
 pub mod game_states;
+pub mod keybind;
 pub mod keybindings;
 pub mod widget;
 pub mod widgets;
@@ -8,3 +9,4 @@ pub use app::{App, Event, GameMode, PerkDecks, View, handle_input_events};
 pub use game_states::{
     GameStates, MainMenuState, PerkDecksState, SettingsState, SkillsConfigState, SkirmishState,
 };
+pub use keybind::handle_keybindings;