Toggle Gravatar support at the system settings.

src/main/twirl/admin/system.scala.html

@@ -19,6 +19,14 @@
               <strong>Deny</strong> - Only administrators can create account.
             </label>
           </fieldset>
+          <hr>
+          <label><strong>Services</strong></label>
+          <fieldset>
+            <label>
+              <input type="checkbox" name="gravatar"@if(settings.gravatar){ checked}/>
+              Gravatar
+            </label>
+          </fieldset>
         </div>
       </div>
       <fieldset>