feat(layout): add front-end application skeleton

refs #59

app/components/ElifeApp.js

+import React from 'react'
+import { Link } from 'react-router-dom'
+
+import { AppBar } from '@pubsweet/ui'
+
+const ElifeApp = ({ children }) => (
+  <div>
+    <AppBar
+      brand={'eLife'}
+      user={{ username: 'Dummy User', admin: true }}
+      onLogoutClick={() => console.log('Logout clicked')}
+      navLinkComponents={[<Link to="/">Dashboard</Link>]}
+    />
+    <div>{children}</div>
+  </div>
+)
+
+export default ElifeApp