Bug 28508: Use "Invoice number" instead of "Invoice no" on the invoice search filter

Bug 28508: Use "Invoice number" instead of "Invoice no" on the invoice search filter

This patch corrects instances of the abbreviated phrase "Invoice no."
from the templates, making it "Invoice number." Also corrected: An
instance of "Bookseller" is replaced with "Vendor."

To test, apply the patch and confirm that the phrase is correct in these
cases:

- Acquisitions -> Invoices: Check the "Search filters" form in the
  left-hand sidebar.
  -> View an invoice: Check the label in the form.
- Acquisitions -> Vendor -> Receive shipments: Check the table of
  invoices.
- Acquisitions -> Orders search (in the search header) -> Advanced
  search: Check the labels in the form.

Signed-off-by: Salman Ali <salman.ali@inLibro.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Note: I fixed Salman's SO line

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>