refactor(SidebarItem): optimizate SidebarItem (#845)

* refactor(sidebar-item): optimizate SiderbarItem.

* chore: update nested examples.

* fix: fix a wrong path.

* fix: fix a transition bug.

* fix: fix a wrong path.

* perf: using "router" mode of el-menu.

* Revert "perf: using "router" mode of el-menu."

This reverts commit cef02a30b0.

* fix: complement i18n text.

src/views/nested/bar/index.vue

@@ -1,7 +0,0 @@
-<template>
-  <div class="app-container">
-    <code>Parent View: Bar</code>
-    <img src="https://wpimg.wallstcn.com/be29a7d2-5ccf-4a2b-888d-8a6c2bbb7aac.png">
-    <router-view></router-view>
-  </div>
-</template>

src/views/nested/bar/posts.vue

@@ -1,6 +0,0 @@
-<template>
-  <div style="margin-top:30px;">
-    <el-alert title="Children: Posts" type="warning" :closable="false">
-    </el-alert>
-  </div>
-</template>

src/views/nested/bar/profile.vue

@@ -1,6 +0,0 @@
-<template>
-  <div style="margin-top:30px;">
-    <el-alert title="Children: Profile" type="success" :closable="false">
-    </el-alert>
-  </div>
-</template>

src/views/nested/menu1/index.vue

@@ -0,0 +1,7 @@
+<template >
+  <div style="padding:30px;">
+    <el-alert title="menu 1" :closable="false">
+      <router-view />
+    </el-alert>
+  </div>
+</template>

src/views/nested/menu1/menu1-1/index.vue

@@ -0,0 +1,7 @@
+<template >
+  <div style="padding:30px;">
+    <el-alert title="menu 1-1" type="success" :closable="false">
+      <router-view />
+    </el-alert>
+  </div>
+</template>

src/views/nested/menu1/menu1-2/index.vue

@@ -0,0 +1,7 @@
+<template>
+  <div style="padding:30px;">
+    <el-alert title="menu 1-2" type="success" :closable="false">
+      <router-view />
+    </el-alert>
+  </div>
+</template>

src/views/nested/menu1/menu1-2/menu1-2-1/index.vue

@@ -0,0 +1,5 @@
+<template functional>
+  <div style="padding:30px;">
+    <el-alert title="menu 1-2-1" type="warning" :closable="false" />
+  </div>
+</template>

src/views/nested/menu1/menu1-2/menu1-2-2/index.vue

@@ -0,0 +1,5 @@
+<template functional>
+  <div style="padding:30px;">
+    <el-alert title="menu 1-2-2" type="warning" :closable="false" />
+  </div>
+</template>

src/views/nested/menu1/menu1-3/index.vue

@@ -0,0 +1,5 @@
+<template functional>
+  <div style="padding:30px;">
+    <el-alert title="menu 1-3" type="success" :closable="false" />
+  </div>
+</template>

src/views/nested/menu2/index.vue

@@ -0,0 +1,5 @@
+<template>
+  <div style="padding:30px;">
+    <el-alert title="menu 2" :closable="false" />
+  </div>
+</template>