ONOS-4359: continued work on theming UI

- replaced masthead logo with double-resolution image.

Change-Id: Ia6ac1a1c1a2870487b60e28ea9c89b69cdfbd979
(cherry picked from commit 9f4303b7)

@@ -39,7 +39,7 @@ html[data-platform='iPad'] #mast {
 
 #mast img.logo {
     height: 47px;
-    width: 436px;
+    width: 511px;
     margin: 0;
 }