Added support for transfering incoming file shares.

- new option --transfer-incoming-shares=1 | 0
- new config.php option 'transfer-incoming-shares' => true | false

The command line option overrules the config.php option.

Signed-off-by: Vincent Petry <vincent@nextcloud.com>
Co-authored-by: Immanuel Pasanec <immanuel.pasanec@compaso.de>