Allow user to change the start/end time without losing work

[icykoneko]

Now that you can edit an existing fish train, the user really ought to be able to edit the start and end times. There's of course a few issues with allowing this, namely, what happens to fish in the schedule that now fall outside the new time bounds? Another problem is a bit more subtle, but will cause trouble at first; FishWatcher and WeatherService. These components really don't like being sent to the past, so if you allow a user to start the train earlier, a LOT of things are going to break; in particular, schedule entries based on catchable range indices. This particular problem still exists if the train is set to start later if the new start date is after the end of a scheduled entry's range. Since it's based on index, you'll need to pay attention to that too (or just remove the entry and not care.) Extending the duration of the train should be fine. Shrinking the during by ending the train earlier should also be fine, but only remove scheduled entries that start AFTER the new end date (we already allow entries that extend beyond the train's end date when based on catchable ranges.)