Bug 14946: Remove C4::Dates from acqui/* files

Bug 14946: Remove C4::Dates from acqui/* files

This patch replaces all use of C4::Dates with Koha::DateUtils, which is
the best practice to follow.

It also fixes a bug on the invoice search, the shipment date (from and
to) were not passed correctly from one page to the other.

Test plan:
1/ Search for orders using the different filters
2/ Create an invoice, try with setting and leaving empty the date
fields.
Default should be an undefined value (not today)
3/ Search for invoices and use the 4 different filters.
Close and reopen invoices.
The filters should be kept from one page to the other (not that it does
not work with shipment date before this patch).
4/ Receive an order, on creating the invoice, the default date should be
today.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>