Refactor CommentedChangeActionDialog to be more reusable

This dialog was refactored out originally to be used
by the revert command, then it got used by the restore
command.  The dialog became a bit messy with way too
many arguments to the constructor and some fields which
were only used once.

This change reduces some of the dialog's functionality
in favor of allowing differentiation to be done via
extending the class instead.  This change also chooses
a few more common defaults for the dialog making it a
bit less cumbersome to setup.  And finally, since the
dialog is a bit more generic and no longer tied to a
change, the file is moved from the change package to the
ui package.

Change-Id: Ic6deabadf4aa983c6632517168fead93623e66f7

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeConstants.java

@@ -113,13 +113,11 @@ public interface ChangeConstants extends Constants {
 
   String buttonRevertChangeBegin();
   String buttonRevertChangeSend();
-  String buttonRevertChangeCancel();
   String headingRevertMessage();
   String revertChangeTitle();
 
   String buttonAbandonChangeBegin();
   String buttonAbandonChangeSend();
-  String buttonAbandonChangeCancel();
   String headingAbandonMessage();
   String abandonChangeTitle();
   String oldVersionHistory();
@@ -135,7 +133,6 @@ public interface ChangeConstants extends Constants {
 
   String buttonRestoreChangeBegin();
   String restoreChangeTitle();
-  String buttonRestoreChangeCancel();
   String headingRestoreMessage();
   String buttonRestoreChangeSend();