fix: add ui when no device is connected

fixes #60

src/routes/config/+layout.svelte

@@ -0,0 +1,17 @@
+<script>
+  import {serialPort} from "$lib/serial/connection"
+  import {LL} from "../../i18n/i18n-svelte"
+</script>
+
+{#if $serialPort}
+  <slot />
+{:else}
+  <p>{$LL.deviceManager.NO_DEVICE()}</p>
+{/if}
+
+<style lang="scss">
+  p {
+    margin: auto;
+    opacity: 0.4;
+  }
+</style>