Add (All, None) selector on environments list

In the comparison page there are selectors on executables and
benchmarks. As we have quite few environents it's good to have the same
selector on the environments list

Author: diegorusso

codespeed/templates/codespeed/comparison.html

@@ -19,12 +19,13 @@
 <div class="sidebox">
   <div class="boxhead"><h2>Environments</h2></div>
   <div class="boxbody">
-    <ul>{% for env in enviros %}
+  <ul><a href="#" class="togglefold">Environments</a> <a href="#" class="checkall">(All</a>, <a href="#" class="uncheckall">None)</a>
+    {% for env in enviros %}
       <li title="{{ env.os }}, {{ env.cpu }}">
         <input id="env_{{ env.id }}" type="checkbox" name="environments" value="{{ env.id }}" />
         <label for="env_{{ env.id }}">{{ env }}</label>
       </li>{% endfor %}
-    </ul>
+  </ul>
   </div>
 </div>
 <div id="executable" class="sidebox">