* 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 cef02a30b02a31242521e9e678cfeaad6f09448c.

* fix: complement i18n text.

* fix filename bug

* format

* format

* refine style

* refine 404 style

* refine

Detail see [Runtime-Compiler-vs-Runtime-only](https://vuejs.org/v2/guide/installation.html#Runtime-Compiler-vs-Runtime-only)

When get rich editor value(null) from backend,it will occur error
```
Error in nextTick: "TypeError: Cannot read property 'replace' of null"
```
So I set val to '' to avoid it

detail see https://panjiachen.github.io/vue-element-admin-site/#/zh-cn/lazy-loading?id=%E8%B7%AF%E7%94%B1%E6%87%92%E5%8A%A0%E8%BD%BD

* refactor: Adjust the example directory structure

* perf form demo

* refine editor-slide-upload css

* refine demo

detail see #534