Bug 29611: Clubs enrollment layout problem in the OPAC

Bug 29611: Clubs enrollment layout problem in the OPAC

This patch makes a minor change to the HTML of the clubs enrollment form
in the OPAC so that the layout works better.

To test you should have at least one club available which allows public
enrollment. The club should have at least one enrollment field
configured.

- Apply the patch and log in to the OPAC.
- On the "Your summary" page, click the "Clubs" tab.
- Click "Enroll" next to the club you configured.
- You should see an enrollment form with the field(s) you configured.
- The "Finish enrollment" button should be styled green and should be
  positioned inside the box which delineates the Clubs tab.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>