Add Some Caching Headers

src/main/kotlin/de/steamwar/routes/Data.kt

@@ -130,6 +130,7 @@ fun Route.configureDataRoutes() {
 
             val skin = getCachedSkin(uuid)
             call.response.header("X-Cache", if (skin.second) "HIT" else "MISS")
+            call.response.header("Cache-Control", "public, max-age=604800")
             call.respondFile(skin.first)
         }