Use utils.defineCustomElement() for defining our custom elements

So we get errors with older browsers.

packages/language-select/.gitmodules

+[submodule "vendor/common"]
+	path = vendor/common
+	url = git@gitlab.tugraz.at:VPU/WebComponents/Common.git

packages/language-select/package.json

@@ -20,7 +20,8 @@
     "rollup-plugin-json": "^4.0.0",
     "rollup-plugin-replace": "^2.2.0",
     "rollup-plugin-multi-entry": "^2.1.0",
-    "i18next-scanner": "^2.10.2"
+    "i18next-scanner": "^2.10.2",
+    "vpu-common": "file:./vendor/common"
   },
   "dependencies": {
     "i18next": "^17.0.3",

packages/language-select/src/demo.js

 import {html, LitElement} from 'lit-element';
 import './language-select.js';
+import utils from 'vpu-common/utils';
 
 class LanguageSelectDemo extends LitElement {
 
@@ -34,4 +35,4 @@ class LanguageSelectDemo extends LitElement {
     }
 }
 
-customElements.define('vpu-language-select-demo', LanguageSelectDemo);
+utils.defineCustomElement('vpu-language-select-demo', LanguageSelectDemo);

packages/language-select/src/language-select.js

 import {html, css, LitElement} from 'lit-element';
 import {i18n, dateTimeFormat, numberFormat} from './i18n.js';
+import utils from 'vpu-common/utils';
 
 /**
  * Emits a vpu-language-changed event where event.detail.lang is the new selected language
@@ -99,4 +100,4 @@ class LanguageSelect extends LitElement {
     }
 }
 
-customElements.define('vpu-language-select', LanguageSelect);
+utils.defineCustomElement('vpu-language-select', LanguageSelect);

common @ 675c681d

+Subproject commit 675c681d7038cce98bbd03fa8483055dd8ef9406