Adding LayoutManager to position videos as cleverly as possible

front/src/WebRtc/HtmlUtils.ts

@@ -0,0 +1,10 @@
+export class HtmlUtils {
+    public static getElementByIdOrFail<T extends HTMLElement>(id: string): T {
+        const elem = document.getElementById(id);
+        if (elem === null) {
+            throw new Error("Cannot find HTML element with id '"+id+"'");
+        }
+        // FIXME: does not check the type of the returned type
+        return elem as T;
+    }
+}