Add <img> to Gefest's primitives

frontend/src/modules/Gefest/primitives/img.ts

@@ -0,0 +1,13 @@
+import { GefestElement } from "../element";
+
+export class GefestImg extends GefestElement {
+    constructor(content : (GefestElement | string)[] | string, src: string) {
+        super(content);
+        this.setAttribute('src', src);
+    }
+
+    protected wrapHTML (content: string): string {
+        const attrString = this.attributesToString();
+        return `<img ${attrString}>${content}</img>`;
+    }
+}