Fix unclickable checkbox in documents view

1. Clicks to the document selection checkbox were captured by the onclick
   handler of the document item header. This is now fixed.

2. Reexpose the doc title link to mouse events by putting it on top of
   the header link layer.

src/documents/templates/admin/documents/document/change_list_results.html

@@ -29,13 +29,32 @@
   .result .header {
     padding: 5px;
     background-color: #79AEC8;
+    position: relative;
   }
-  .result .header .checkbox{
+  .result .header .checkbox {
     width: 5%;
     float: left;
+    position: absolute;
+    z-index: 2;
   }
   .result .header .info {
     margin-left: 10%;
+    position: relative;
+  }
+  .headerLink {
+    cursor: pointer;
+    opacity: 0;
+    z-index: 1;
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+  }
+  .header > a {
+    z-index: 2;
+    margin-left: 10%;
+    position: relative;
   }
   .result .header a,
   .result a.tag {
@@ -136,12 +155,23 @@
     {# 7: Document edit url #}
     <div class="box">
       <div class="result">
-        <div class="header" onclick="location.href='{{ result.7 }}';" style="cursor: pointer;">
+        <div class="header">
+          {% comment %}
+            The purpose of 'headerLink' is to make the whole header
+            background clickable.
+            We use an onclick handler here instead of a native link ('<a>')
+            to allow selecting (and copying) the overlying doc title text
+            with the mouse cursor.
+            If the title link were layered upon another link ('<a>'), title text
+            selection would not be possible with mouse click + drag. Instead,
+            the underlying link would be dragged.
+          {% endcomment %}
+          <div class="headerLink" onclick="location.href='{{ result.7 }}';"></div>
           <div class="checkbox">{{ result.0 }}</div>
           <div class="info">
-            {{ result.5 }}<br />
-            {{ result.1 }}
+            {{ result.5 }}
           </div>
+          {{ result.1 }}
           <div style="clear: both;"></div>
         </div>
         <div class="tags">{{ result.6 }}</div>