states: Add a "Game Over" state

Add a game over state where the player can choose to start a new game or
quit.

src/states/game_over.rs

+use crate::gamestate;
+use crate::states;
+use crate::utils;
+
+pub struct GameOverState {
+    gui_svg: web_sys::SvgElement,
+}
+
+impl GameOverState {
+    pub fn new() -> GameOverState {
+        GameOverState {
+            gui_svg: utils::get_element_by_id("game-over-ui").unwrap(),
+        }
+    }
+}
+
+impl gamestate::State for GameOverState {
+    fn init(&mut self, mut init: gamestate::StateInitializer) -> gamestate::Transition {
+        init.register_onclick("game-over-replay");
+        init.register_onclick("game-over-quit");
+        self.gui_svg
+            .style()
+            .set_property("display", "block")
+            .unwrap();
+
+        gamestate::Transition::Sleep
+    }
+
+    fn deinit(&mut self) {
+        self.gui_svg
+            .style()
+            .set_property("display", "none")
+            .unwrap();
+    }
+
+    fn event(&mut self, event: gamestate::Event) -> gamestate::Transition {
+        match event {
+            gamestate::Event::MouseClick {
+                target: "game-over-replay",
+                ..
+            } => gamestate::Transition::push(states::HeavenState::new(None)),
+            gamestate::Event::MouseClick {
+                target: "game-over-quit",
+                ..
+            } => gamestate::Transition::Pop,
+            event => {
+                crate::console_warn!("unknown event {:?}", event);
+                gamestate::Transition::Keep
+            }
+        }
+    }
+}

src/states/mod.rs

+mod game_over;
 mod heaven;
 mod ingame;
 mod level_loading;
 mod main_menu;
 
+pub use game_over::GameOverState;
 pub use heaven::HeavenState;
 pub use ingame::InGameState;
 pub use level_loading::LevelLoadingState;

www/src/index.html

@@ -89,6 +89,21 @@
           <text x="0" y="0">START SHIFT</text>
         </g>
       </svg>
+      <svg id="game-over-ui" class="game-gui" viewBox="0 0 1920 1080" style="display: none">
+        <!-- GUI for the Game Over screen -->
+        <rect x="0" y="0" width="1920" height="1080" class="background" />
+
+        <text x="960" y="300" class="header">Game Over</text>
+
+        <g id="game-over-replay" transform="translate(960, 500)" class="big-button button-1">
+          <rect x="-350" y="-60" width="700" height="120" />
+          <text x="0" y="0">Start New Game</text>
+        </g>
+        <g id="game-over-quit" transform="translate(960, 650)" class="big-button button-3">
+          <rect x="-120" y="-60" width="240" height="120" />
+          <text x="0" y="0">Quit</text>
+        </g>
+      </svg>
       <svg id="menu-ui" class="game-gui" viewBox="0 0 1920 1080" style="display: block">
         <!-- GUI for the main menu -->
         <rect x="0" y="0" width="1920" height="1080" class="background" />