Feature/mixpanel update 28 7

There's a 1% PR that uses this code. 
You should do the errors / success using promises:

        var _this = this;
        return App.Project.find(project_id).then(function() {
            if (_this.get('tracker')) {
                _this.get('tracker').trackEvent("Project detail", {"project id": page.get('id')});
            }
        }, function() {
            _this.transitionTo('projectList');
        });