Improve accessibility: wrap logo in div not H1 (#2844)

Author: hugovk

static/sass/style.css

@@ -1078,7 +1078,6 @@ h2.not-column {
     text-align: center;
     padding: .75em 1em; }
 
-/*h1*/
 .site-headline {
   color: white;
   margin: 0.15em auto 0.2em; }

static/sass/style.scss

@@ -411,7 +411,7 @@ h2.not-column {
     }
 }
 
-/*h1*/ .site-headline {
+.site-headline {
     color: $white;
     margin: 0.15em auto 0.2em;
 

templates/base.html

@@ -185,9 +185,9 @@
         <header class="main-header" role="banner">
             <div class="container">
 
-                <h1 class="site-headline">
+                <div class="site-headline">
                     {% block section-logo %}<a href="/"><img class="python-logo" src="{{ STATIC_URL }}img/python-logo.png" alt="python&trade;"></a>{% endblock %}
-                </h1>
+                </div>
 
                 <div class="options-bar-container do-not-print">
                     <a href="https://donate.python.org/" class="donate-button">Donate</a>