Bug 26735: Overdrive login modal broken in the OPAC

Bug 26735: Overdrive login modal broken in the OPAC

This patch makes corrections to the markup for the Overdrive login modal
in the OPAC. It hadn't been updated during the upgrade to Bootstrap 4.

To test, apply the patch and enable the system
preferences required for Overdrive integration.

- Log in to the OPAC.
- On the "Your summary" page open the "OverDrive Account" tab.
- Click the "Log in to your OverDrive account" link.
- The modal should appear and look correct.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>