Add CWL header image and link to it internally

Fixes https mixed content errors on https://view.commonwl.org

Author: Mark Robinson

src/main/resources/static/img/CWL-Logo-Header.png

@@ -28,7 +28,7 @@
     <div class="container">
         <div class="navbar-header">
             <a class="navbar-brand" href="/">
-                <img id="logo" src="http://www.commonwl.org/CWL-Logo-Header.png"></img>
+                <img id="logo" src="/img/CWL-Logo-Header.png"></img>
             </a>
         </div>
     </div>