feat(ionTab): add class attribute to tab items

js/angular/directive/tab.js

@@ -64,6 +64,7 @@ function($rootScope, $animate, $ionicBind, $compile) {
         attrStr('icon-off', attr.iconOff) +
         attrStr('badge', attr.badge) +
         attrStr('badge-style', attr.badgeStyle) +
+        attrStr('class', attr.class) +
         '></ion-tab-nav>';
 
       //Remove the contents of the element so we can compile them later, if tab is selected