Bug 16540 - Clean up opac-auth.tt for translatability

Bug 16540 - Clean up opac-auth.tt for translatability

This patch fixes translatability issues in opac-auth.tt (ugly
translations caused by sentence splitting).

It was necessary to change indentation to make the the file more
readable and to make sure that changes have no side effects.

The changes do not touch the overall functionallity.

To test:
- Review code to verify that no functionality change is introduced
  and to verify that the text changes make sense.
- Apply patch, verify that OPAC login page behaves as before.

UPDATE: Amended for comment #10 / mv
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 6b432d2b213101d2e8d0bf41fbc4a0e5b4ecb4e1)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>