[feladat @ 115] Fixed a missing slash in a html tag in list_zones.php.

[feladat @ 114] Patch for ticket 19. Because of the use of the quote function, empty strings where converted to NULL as MDB2_PORTABILITY_EMPTY_TO_NULL is set by default. This problem also applied to the active state of an user.

[feladat @ 113] Password field in users.php is now set to type 'password' instead of 'text'. When typing password '*' are shown instead of the password.