Refactor login form elements code duplication

[Ruslan Kabalin]

All login form elements along with extra login form elements are declared twice, in auth_get_login_form() and auth_generate_login_form() respectively. The differences are really minor, so I suggest to move login form elements generation to separate function, making it less prone to errors.

auth_get_login_form() - used when logged-off user tries to access something different from main page or session has expired.
auth_generate_login_form() - used in side-block on the main page

The auth_get_login_form() version of login form is missing (see attached diff):

* 'defaultvalue' is missing in 'login_username' - can be used, nothing major
* 'login_password' is not regarded as 'required' field here for some reason...
* Register link is not shown - I do not see a reason why it should not be displayed
* Login container is missing 'login' class - can be added, does not break styles

[Ruslan Kabalin (rkabalin)]

Discovered while fixing bug #1023791

[Ruslan Kabalin (rkabalin)]

Ready for revision: https://reviews.mahara.org/#/c/1409/

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/1409
Committed: http://gitorious.org/mahara/mahara/commit/eb6d0ab826a7be0f04e1e708fa5bb129c0fc542c
Submitter: Ruslan Kabalin (<email address hidden>)
Branch: master

commit eb6d0ab826a7be0f04e1e708fa5bb129c0fc542c
Author: Ruslan Kabalin <email address hidden>
Date: Thu Jul 12 11:30:20 2012 +0100

    Refactor login form elements (bug #1023834)

    This patch moves form elements array to the separate function.

    Change-Id: I546017bc59d64716d2498a9263c44188fe1274ee
    Signed-off-by: Ruslan Kabalin <email address hidden>