ui: make coll-index more extensible

update CHANGES.md
update to latest wombat
bump version to 1.3.3

src/coll-index.js

@@ -282,7 +282,7 @@ class WrCollIndex extends LitElement
         ` : html`
 
         <div class="panel-block extra-padding">
-          <i>No Archives so far! Archives loaded in the section above will appear here.</i>
+        ${this.renderEmpty()}
         </div>
         `}
       </div>
@@ -293,6 +293,10 @@ class WrCollIndex extends LitElement
   renderCollInfo(coll) {
     return html`<wr-coll-info .coll=${coll}></wr-coll-info>`;
   }
+
+  renderEmpty() {
+    return html`<i>No Archives so far! Archives loaded in the section above will appear here.</i>`;
+  }
 }