add layout (#6600)

* add layout

* add docs

* add en docs

* fix test

packages/header/index.js

@@ -0,0 +1,8 @@
+import Header from './src/main';
+
+/* istanbul ignore next */
+Header.install = function(Vue) {
+  Vue.component(Header.name, Header);
+};
+
+export default Header;

packages/header/src/main.vue

@@ -0,0 +1,20 @@
+<template>
+  <header class="el-header" :style="{ height }">
+    <slot></slot>
+  </header>
+</template>
+
+<script>
+  export default {
+    name: 'ElHeader',
+
+    componentName: 'ElHeader',
+
+    props: {
+      height: {
+        type: String,
+        default: '60px'
+      }
+    }
+  };
+</script>