Add option to match author timestamp and committed timestamp

When true, the author date is changed to match the submitter date
upon submission of a change. This is done so that git log will show
the submission date instead of the author date, which it does by
default.

This option only takes effect in submit strategies which already modify
the commit, i.e. Cherry Pick, Rebase Always, and (perhaps) Rebase If
Necessary.

Bug: https://crbug.com/732968
Change-Id: I64133a3e494e8c6364cd210f68979aaff74cb222

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/AdminConstants.java

@@ -77,6 +77,8 @@ public interface AdminConstants extends Constants {
 
   String enableReviewerByEmail();
 
+  String matchAuthorToCommitterDate();
+
   String headingMaxObjectSizeLimit();
 
   String headingGroupOptions();