feat(loading): add loading screen as web component

public/scan-loading-screen/scan-loading-screen.js

@@ -0,0 +1,21 @@
+class ScanLoadingScreen extends HTMLElement {
+    constructor() {
+        super();
+        const shadowRoot = this.attachShadow({mode: 'open'});
+        const link = document.createElement('link');
+        link.rel = 'stylesheet';
+        link.href = '/scan-loading-screen/scan-loading-screen.css';
+        const container = document.createElement('div');
+        container.classList.add('container');
+        const barcode = document.createElement('div');
+        barcode.classList.add('barcode');
+        for(let i = 0; i < 30; i++) {
+            const div = document.createElement('div');
+            barcode.appendChild(div);
+        }
+        container.appendChild(barcode);
+        shadowRoot.appendChild(link);
+        shadowRoot.appendChild(container);
+    }
+}
+customElements.define('scan-loading-screen', ScanLoadingScreen);