For the same reasons as with expenses[0], users are no longer expected
to manually set invoice status, and is now linked to their collections.
In this case, however, we had to remove the ‘sent’ and ‘unpaid’ status
options, because these _should_ only be set manually, as there is no
way for the application to know when to set them. Thus, there could
be inconsistencies, like invoices set to ‘unpaid’ when they actually
have collections, or invoices that were ‘sent’, then transitioned to
‘partial’/‘paid’ due to a collection, but then reset to ‘created’ if the
collection was deleted.
[0]: ac0143b2b0
jordi fita mas