Optimize pngs

 modules/header/images/wikipedia-logo-landscape.png | Bin 16578 -> 14382 bytes
 modules/tools/images/link_lightgray.png            | Bin 18971 -> 9444 bytes
 modules/tools/images/pasting.png                   | Bin 382 -> 372 bytes
 modules/tools/images/search.png                    | Bin 1055 -> 989 bytes

Change-Id: Id1dc04dfa5b62630d287967a05a6bfea6494f80d