ref(toolbar): re-wrap buttons for torture tests

The inline classes for the toolbars were re-arranged
to fix non-rounded corners in the always-on-top window's
toolbar. However, those classes were also used by the
torture tests as a way to find stable elements that will
not get blown away by a react re-render. So re-wrap the
buttons with a div that will not get blown away,
add back the inline classes to those divs, and change
the CSS to round the corners in the always-on-top
window's toolbar.

css/_toolbars.scss

 
         @include transform(translateX(-50%));
 
+        > a:first-child.button,
         > div:first-child .button {
             border-bottom-left-radius: 3px;
             border-top-left-radius: 3px;
         }
+
+        > a:last-child.button,
         > div:last-child .button {
             border-bottom-right-radius: 3px;
             border-top-right-radius: 3px;

react/features/toolbox/components/StatelessToolbarButton.js

         const attributes = getButtonAttributesByProps(button);
 
         return (
-            <div className = { `toolbar-button-wrapper ${button.id}-wrapper` }>
+            <div className = 'toolbar-button'>
                 <a
                     { ...attributes }
                     onClick = { this._onClick }>

react/features/toolbox/components/ToolbarButton.web.js

             );
         }
 
-        return children;
+        return (
+            <div className = { `toolbar-button-wrapper ${button.id}-wrapper` }>
+                { children }
+            </div>
+        );
     }
 
     /**