Improve the link meaning.

dream/platform/src2/dream/index.html

@@ -52,8 +52,8 @@
         <a href="#leftpanel"
            data-icon="bars"
            class="menu_link ui-btn ui-icon-bars ui-btn-icon-left">Menu</a>
-        <a data-icon="back"
-           class="back_link ui-btn ui-icon-back ui-btn-icon-right">Back</a>
+        <a data-icon="carat-u"
+           class="back_link ui-btn ui-icon-carat-u ui-btn-icon-left">Parent</a>
       </div>
       <h1>Dream Simulation</h1>