Use higher res logo icon

app/experimenter/static/css/adminextra.css

@@ -4,7 +4,8 @@ body {
 }
 
 .header_logo_icon {
-	height: 1.5em;
+	height: 1.7em;
+  margin-top: -5px;
   padding-right: 5px;
 }
 

app/experimenter/templates/admin/base_site.html

@@ -10,5 +10,5 @@
 {% endblock %}
 
 {% block branding %}
-<h1 id="site-name"><a href="{% url 'admin:index' %}"><img class="header_logo_icon" src="{% static "imgs/favicon_32_white.png" %}" />Mozilla Experimenter</a></h1>
+<h1 id="site-name"><a href="{% url 'admin:index' %}"><img class="header_logo_icon" src="{% static "imgs/favicon_128_white.png" %}" />Mozilla Experimenter</a></h1>
 {% endblock %}