Invalid timestamp for persistent notification (Closes #123)

I've found out that setting `persistentNotification.when = -Long.MAX_VALUE` makes date TextView look like `28.11.17`. I've just tested [the code](https://github.com/android/platform_frameworks_base/blob/master/core/java/android/widget/DateTimeView.java) that renders it. So I've changed the constant to 0, it works on API level 10 (hides the timestamp), maybe needs more testing though. Please refer to this [question](http://stackoverflow.com/questions/5757997/hide-time-in-android-notification-without-using-custom-layout) for more info.