show email only if available
<i class="fa fa-sign-in"></i> Login
</md-button>
<div v-if="$store.state.user" md-right>
- {{ $store.state.user.username }} ({{$store.state.user.email }})
+ {{ $store.state.user.username }} <div v-if="$store.state.user.email">({{ $store.state.user.email }})</div>
</div>
</md-toolbar>
