Add allowed_classes restriction to unserialize() calls

Add allowed_classes => false to unserialize() in filter_api.php and
email_queue_api.php.

Add $p_options parameter to safe_unserialize().

Update 3 safe_unserialize() calls in install_helper_functions_api.php
to pass ['allowed_classes' => false], consistent with the changes in
filter_api.php and email_queue_api.php.

Fixes 0037219, PR https://github.com/mantisbt/mantisbt/pull/2229

Co-authored-by: XananasX7 xananasX7@users.noreply.github.com