We only want two statuses for expense: not yet paid (pending), and paid.
Thus, it is a bit different from quotes and invoices, because expenses
do not pass throw the “workflow” of created→sent→{pending,paid}. That’s
way in this case the status field is already in the new expense form,
instead of hidden, and by pending is not equivalent to created but
unpaid (i.e., the same status color).
With the new select field in the form, the file field no longer can
span two columns or it would be alone on the next row.
Closes#67.
jordi fita mas