Add style for selected menu item

@ghislaineguerin please review. This is in relation to https://trello.com/c/WaINVqZD/76-highlight-navigation-selection-to-indicate-to-the-user-what-page-you-re-on

The idea is that `selected` class will be added dynamically to the selected menu item. For example:
```
<div class="navbar-collapse navbar-left hidden-xs hidden-sm">
	<ul class="nav navbar-nav">
		<li>
			<a ng-href="#/" class="selected" href="#/">Store</a> 
		</li>
	</ul>
</div>
```