Allow bulk updating of order statuses

This allows updating more than one order's status, similar to how line
statuses of an order can be updated.

This commit is a squashed version of the changes in #1391.
Tweak order status bulk updating

I've slightly refactored the changes introduced in the previous commit.
Removed setting line statuses in the sandbox because for most basic
scenarios, such fine-grained control is probably not necessary. And more
advanced scenarios want a custom pipeline anyway.

Closes #1391.
Remove unused current_view attribute on views

Must be a left-over from removed logic, and is not used. It's a bad name
as well, as it really is the primary URL name.

I'm not opposed to views knowing about their primary URL name though.
But if that's implemented, it should tie in with the Application class.