refactored tab activation

src/public/javascripts/widgets/tab_caching_widget.js

@@ -35,6 +35,14 @@ export default class TabCachingWidget extends TabAwareWidget {
         return false; // stop propagation to children
     }
 
+    tabRemovedListener({tabId}) {
+        const widget = this.widgets[tabId];
+
+        if (widget) {
+            widget.remove();
+        }
+    }
+
     toggle(show) {
         for (const tabId in this.widgets) {
             this.widgets[tabId].toggle(show && this.tabContext && tabId === this.tabContext.tabId);