fix(dialog): reintroduced dialogOpenClass option

This option represents  class which is added to the body when the dialog is open.
It was present before in twitter bootstrap, then removed in 2.3.0,
but then recently reintroduced in 3.0

Closes angular-ui#798

Author: Louis Sivillo

src/dialog/dialog.js

@@ -20,6 +20,7 @@ dialogModule.provider("$dialog", function(){
     backdropClass: 'modal-backdrop',
     transitionClass: 'fade',
     triggerClass: 'in',
+    dialogOpenClass: 'modal-open',
     resolve:{},
     backdropFade: false,
     dialogFade:false,
@@ -133,7 +134,7 @@ dialogModule.provider("$dialog", function(){
           if(self.options.dialogFade){ self.modalEl.addClass(self.options.triggerClass); }
           if(self.options.backdropFade){ self.backdropEl.addClass(self.options.triggerClass); }
         });
-
+        body.addClass(defaults.dialogOpenClass);
         self._bindEvents();
       });
 
@@ -191,7 +192,7 @@ dialogModule.provider("$dialog", function(){
     Dialog.prototype._onCloseComplete = function(result) {
       this._removeElementsFromDom();
       this._unbindEvents();
-
+      body.removeClass(defaults.dialogOpenClass);
       this.deferred.resolve(result);
     };