Propagate shadow expiry from user templates to created user objects.

[sunweaver]

No description provided.

[master-caster]

The following code seems to do the same with the exception
that it will only show the checkbox if shadowExpire is in the future.

    /* Only enable checkbox, if shadowExpire is in the future */
    if($this->shadowExpire > time()) {
      $this->activate_shadowExpire= "1";
    }

With this PR

$this->activate_shadowExpire= "1";

gets always executed if shadowExpire isn't 0.
Do we need the code that follows if we don't care about the value in shadowExpire?