This was requested by Oriol; there are no other technical or legal
requirements for this.
I can not simply append the customer name to the file because it could
have characters that are not valid in file name depending on the
operating system, so i have to “slugify” it.
Closes#65
There was no explicit `order by` in the queries that list the products
of quotes and invoices, so PostgreSQL was free to use any order it
wanted. In this case, since was am grouping first by name, the result
was sorted by product name.
This is not an issue in most cases, albeit a bit rude to the user,
except for when the products *have* to in the same order the user
entered them, because they are monthly fees or something like that, that
must be ordered by month _number_, not by their _name_; the user will
usually input them in the correct order they want them on the invoice or
quote.
Sorting by *_product_id does *not* guarantee that they will always be
in insertion order, because the sequence can “wrap”, but i think i am
going to have bigger problems at that point.
jordi fita mas