代码优化，结构调整，进度50%

src/layout/components/index.js

@@ -0,0 +1,5 @@
+export { default as Navbar } from './Navbar'
+export { default as Sidebar } from './Sidebar'
+export { default as AppMain } from './AppMain'
+export { default as TagsView } from './TagsView'
+export { default as Settings } from './Settings'