Adds a status class for noting when warnings are present.

The status class, `.has-warning`, provides a hook for other content to adjust
their positioning. It's leveraged to push down the absolutely positioned chapter
navs far enough so that they clear both the warning message and the icons in the
header bar. Fixes #656.

second-edition/theme/index.hbs

@@ -20,7 +20,12 @@
         <link rel="stylesheet" href="highlight.css">
         <link rel="stylesheet" href="tomorrow-night.css">
         <style>
-            p.warning {	
+            .page-wrapper.has-warning > .nav-chapters {
+              /* add height for warning content & margin */
+              top: 120px;
+            }
+
+            p.warning {
                 background-color: rgb(242, 222, 222);
                 border-bottom-color: rgb(238, 211, 215);
                 border-bottom-left-radius: 4px;
@@ -91,7 +96,7 @@
             {{#toc}}{{/toc}}
         </div>
 
-        <div id="page-wrapper" class="page-wrapper">
+        <div id="page-wrapper" class="page-wrapper has-warning">
 
             <div class="page">
                 <header><p class="warning">You are reading a <strong>draft</strong> of the next edition of TRPL. For more, go <a href="../index.html">here</a>.</p></header>