Add support for diff web links

Plugins can now add web links to the diff screen that will be
displayed next to the navigation icons.

Change-Id: Ifa01103054c3e81e3121c219ee5b69db2fefb3bf
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffApi.java

@@ -63,6 +63,11 @@ public class DiffApi {
     return this;
   }
 
+  public DiffApi webLinksOnly() {
+    call.addParameter("weblinks-only", true);
+    return this;
+  }
+
   public DiffApi ignoreWhitespace(AccountDiffPreference.Whitespace w) {
     switch (w) {
       default: