Add error handling for missing icons and clean up the template

packages/common/vpu-icon.js

 import {html, LitElement, css} from 'lit-element';
 import {until} from 'lit-html/directives/until.js';
-import {unsafeHTML} from 'lit-html/directives/unsafe-html.js';
 import * as commonUtils from './utils.js';
 
 /**
@@ -32,10 +31,17 @@ class Icon extends LitElement {
 
     render() {
         let svg = fetch('local/vpu-common/icons/' + this.name + '.json').then(response => {
+            if (!response.ok)
+                throw Error(response.statusText);
             return response.json().then(data => {
-                return unsafeHTML('<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" style="pointer-events: none; display: block; width: 100%; height: 100%;">' +'<path d="' + data + '" />' + '</svg>');
+                return html`
+                    <svg aria-labelledby="title" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" style="pointer-events: none; display: block; width: 100%; height: 100%;">
+                        <title id="title">${this.name}</title>
+                        <path d=${data} />
+                    </svg>
+                `;
             });
-        })
+        });
 
         return html`
             <style>