Get rid of date on generated code

[krico]

The slim3 generated code has this annoying @javax.annotation.Generated that has the date, this causes conflicts if two devs generate in paralel.

package com.jasify.schedule.appengine.meta.payment;

//@javax.annotation.Generated(value = { "slim3-gen", "@VERSION@" }, date = "2015-03-22 13:08:07")
/** */
public final class PaymentMeta extends org.slim3.datastore.ModelMeta<com.jasify.schedule.appengine.model.payment.Payment> {
...
}