Status options in the subscription edit screen

A regular user gets three status options in the edit screen for her subscriptions (user/N/notifications/subscriptions/edit/NNN):
- active
- inactive
- disabled
(The 'blocked' status is properly filtered out. The 'disabled' status isn't.)

This is unclear (and I'm placing this in production) so I wanted to get rid of the 'disabled' status.

First I thought, let's just scrap 'disabled' in this screen always, and scrap the links to the edit screen (from the overview) for 'disabled' subscriptions, and be done with it.

On second thought, there's a different solution... one really shouldn't be able to change individual subscriptions from active <-> disabled. So this patch always filters out one of those 2 options. I also included a more elaborate description, in case 'disabled' is among the choices.

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Issues:

- There's one thing that is not accounted for yet: changint disabled->active subscriptions 'in bulk', in the user/N/notifications/subscriptions list. Should that be prevented too? (I'll include this in the patch somehow if you want me to, but that's not urgent for my site.)

- The order of options has 'blocked' as the 2nd choice. I'd like it to be 4th (or 3rd) so active/inactive are always adjacent.
Am I allowed to change the order in Notifications_Subscription::status_list()? :-)