Move enum from yew_components mod to state mod

Preparation for symlinking shared code into the backend project.

front_end/src/state.rs

@@ -1,5 +1,4 @@
 use crate::ai::AIDifficulty;
-use crate::yew_components::MainMenuMessage;
 use std::cell::Cell;
 use std::fmt::Display;
 use std::rc::Rc;
@@ -288,3 +287,12 @@ impl Default for SharedState {
         }
     }
 }
+
+// This enum moved from yew_components module so that this module would have no
+// dependencies on the yew_components module
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum MainMenuMessage {
+    SinglePlayer(Turn, AIDifficulty),
+    LocalMultiplayer,
+    NetworkedMultiplayer(Turn),
+}

front_end/src/yew_components.rs

@@ -5,7 +5,7 @@ use crate::html_helper::{
     append_to_info_text, element_append_class, element_remove_class, get_window_document,
 };
 use crate::random_helper::get_seeded_random;
-use crate::state::{BoardState, GameState, SharedState, Turn};
+use crate::state::{BoardState, GameState, MainMenuMessage, SharedState, Turn};
 
 use std::cell::Cell;
 use std::rc::Rc;
@@ -18,12 +18,6 @@ use yew::prelude::*;
 
 pub struct MainMenu {}
 
-pub enum MainMenuMessage {
-    SinglePlayer(Turn, AIDifficulty),
-    LocalMultiplayer,
-    NetworkedMultiplayer(Turn),
-}
-
 impl Component for MainMenu {
     type Message = MainMenuMessage;
     type Properties = ();