feat:新增功能

1.Dashboard下增加子菜单：Panel、MetricPreview
2.Panel菜单下完成以下功能
   （1）panel列表展示中的新增功能
   （2）panel列表展示中对应记录的删除和修改功能
   （3）Add按钮的新增panel功能
3.MetricPreview菜单完成了左侧列表的跳转功能

nezha-fronted/src/router/index.js

@@ -21,6 +21,14 @@ export default new Router({
           path: '/dashboard',
           component: resolve => require(['../components/page/dashboard.vue'], resolve),
         },
+        {
+          path: '/panel',
+          component: resolve => require(['../components/page/dashboard/panel.vue'], resolve),
+        },
+        {
+          path: '/metricPreview',
+          component: resolve => require(['../components/page/dashboard/metricPreview.vue'], resolve),
+        },
         {
           path: '/project',
           component: resolve => require(['../components/page/project/project.vue'], resolve),