Add LoginForm.

src/components/login_form/login_form.js

+const LoginForm = {
+  data: () => ({
+    user: {}
+  }),
+  computed: {
+    loggingIn () { return this.$store.state.users.loggingIn }
+  },
+  methods: {
+    submit () {
+      this.$store.dispatch('loginUser', this.user)
+    }
+  }
+}
+
+export default LoginForm

src/components/login_form/login_form.vue

+<template>
+  <div class="panel panel-default">
+    <!-- Default panel contents -->
+    <div class="panel-heading">
+      Log in
+    </div>
+    <div class="panel-body">
+      <form v-on:submit.prevent='submit(user)'>
+        <div class='form-group'>
+          <label for='username'>Username</label>
+          <input :disabled="loggingIn" v-model='user.username' class='form-control' id='username' placeholder='e.g. lain'>
+        </div>
+        <div class='form-group'>
+          <label for='password'>Password</label>
+          <input :disabled="loggingIn" v-model='user.password' class='form-control' id='password' type='password'>
+        </div>
+        <div class='form-group'>
+          <button :disabled="loggingIn" type='submit' class='btn btn-default'>Submit</button>
+        </div>
+      </form>
+    </div>
+  </div>
+</template>
+
+<script src="./login_form.js" ></script>