Fix up the backend so it has sane names like get_sprite and get_icon, then implemented a guecs::Icon for icons. Those don't scale and typically have other properties different from a Sprite.

include/guecs/sfml/components.hpp

@@ -38,12 +38,16 @@ namespace guecs {
   };
 
   struct Sprite {
-    // either you set a filename here,
-    // or some kind of config,
-    // or a callback that does the loading,
-    // or a virtual function and you subclass
-    // or there's a static config function you call once,
-    // that's passed an object with all the necessary gear
+    string name;
+    int padding = THEME.PADDING;
+    std::shared_ptr<sf::Sprite> sprite = nullptr;
+
+    void init(lel::Cell &cell);
+    void update(const string& new_name);
+    void render(sf::RenderWindow& window, sf::Shader *shader_ptr);
+  };
+
+  struct Icon {
     string name;
     int padding = THEME.PADDING;
     std::shared_ptr<sf::Sprite> sprite = nullptr;