Support custom effective date for fee check command

Added support to specify custom effective date to run the fee check command.
Such functionality is useful for TLDs with creation price as a function of
time, such as those with EAP. However the implementation is not limited EAP or
create price check. Any fee check can specify a date, as long as its XML schema
supports a date.

Currently conforming to fee extension v12, subject to schema changes.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133420255

java/google/registry/model/domain/fee06/FeeInfoCommandExtensionV06.java

@@ -14,11 +14,13 @@
 
 package google.registry.model.domain.fee06;
 
+import com.google.common.base.Optional;
 import google.registry.model.domain.fee.FeeQueryCommandExtensionItemImpl;
 import google.registry.model.eppinput.EppInput.CommandExtension;
 import javax.xml.bind.annotation.XmlRootElement;
 import javax.xml.bind.annotation.XmlType;
 import org.joda.money.CurrencyUnit;
+import org.joda.time.DateTime;
 
 /** A fee extension that may be present on domain info commands. */
 @XmlRootElement(name = "info")
@@ -33,5 +35,10 @@ public class FeeInfoCommandExtensionV06
   public CurrencyUnit getCurrency() {
     return currency;
   }
+  
+  @Override
+  public Optional<DateTime> getEffectiveDate() {
+    return Optional.absent();
+  }
 }