Hide the logo and fork me img on XS screens

They take too much space

templates/default/public_toolbar.html.ep

@@ -1,6 +1,6 @@
   <nav class="navbar navbar-default" role="navigation">
     <a href="https://github.com/dani/vroom">
-      <img id="forkMeRibbon" src="/img/fork_me_on_gh.png" alt="Fork me on GitHub">
+      <img id="forkMeRibbon" src="/img/fork_me_on_gh.png" alt="Fork me on GitHub" class="hidden-xs"/>
     </a>
     <div class="container-fluid">
       <div class="navbar-header">
@@ -8,7 +8,7 @@
           <span class="sr-only"></span>
           <span class="glyphicon glyphicon-th"></span>
         </button>
-        <a href="#"><img id="navBarLogo" src="/img/logo_vroom_alpha.png"/></a>
+        <a href="#"><img id="navBarLogo" src="/img/logo_vroom_alpha.png" class="hidden-xs"/></a>
       </div>
       <div class="collapse navbar-collapse" id="toolBar">
         <ul class="nav navbar-nav navbar-right">