Bug 27681: Style OPAC self-registration CAPTCHA as uppercase

Bug 27681: Style OPAC self-registration CAPTCHA as uppercase

This patch adds an inline "text-transform:uppercase" style attribute to
the OPAC self-registration CAPTCHA field so that the user doesn't have
to match the case of the CAPTCHA they're shown.

To test, apply the patch and start the process of self-registration in
the OPAC.

- At the end of the form, under verification, confirm that any text you
  type in the verification field is uppercase by default.
- Confirm that the CAPTCHA is accepted when you submit the form.

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>