add findShipDef/findModuleDef/findRecipeDef to config structs and re-use them in the rest of the code base

src/lib/config/ShipsConfig.h

@@ -49,4 +49,18 @@ struct ShipDef
 struct ShipsConfig
 {
     std::vector<ShipDef> ships;
+
+    // Returns the definition for the given ship schematic id, or nullptr if the
+    // id has no entry in ships.toml.
+    const ShipDef* findShipDef(const std::string& id) const
+    {
+        for (const ShipDef& def : ships)
+        {
+            if (def.id == id)
+            {
+                return &def;
+            }
+        }
+        return nullptr;
+    }
 };