Bug 28079: Set focus to search box field when adding an order to basket

Bug 28079: Set focus to search box field when adding an order to basket

This patch modifies the "Add to basket" modal in acquisitions so that
focus is automatically moved to the first form field when the modal
appears.

The patch also corrects the modal markup so that it's more consistent
with default Bootstrap markup.

To test, apply the patch and go to Acquisitions.

- Search for a vendor and, if necessary, create a basket.
- Click the "Add to basket" button. The modal which appears should
  have a header reading "Add order to basket <basketname>"
- The form field should have cursor focus.
- View the basket and click the "Add to basket" button in the toolbar.
- The modal shown should also be correct.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>