client: Fix calendar dropdown not closing (fixes #384)

The regression was introduced in 612e440.
This might cause some other issues in closing the highlights, but none
were identified during a cursory testing.

src/public/app/widgets/buttons/onclick_button.js

@@ -7,7 +7,6 @@ export default class OnClickButtonWidget extends AbstractButtonWidget {
 
         if (this.settings.onClick) {
             this.$widget.on("click", e => {
-                e.stopPropagation();
                 this.$widget.tooltip("hide");
 
                 this.settings.onClick(this, e);