feat(modal): remove an unnecessary $digest

Optimized opening of modals by causing one digest loop less: The modalBackdrop directive now schedules switching its animate flag using a $timeout which does not cause a digest loop. If we assume modalBackdrop is always followed by a modalWindow directive, then we are guaranteed a digest loop by modalWindow's $timeout, which will happen after modalBackdrop's $timeout.

src/modal/modal.js

@@ -67,10 +67,11 @@ angular.module('ui.bootstrap.modal', [])
 
         scope.animate = false;
 
-        //trigger CSS transitions
+        // schedule to trigger CSS transitions, but skip invoking apply immediately
+        // (modalWindow's $timeout will invoke an apply which is enough since modalWindow is added after modalBackdrop)
         $timeout(function () {
           scope.animate = true;
-        });
+        }, 0, false);
       }
     };
   }])