add a optional parameter to skip check for expired files, this is necessary to find out to whom a file was shared after it was expired.

Use a DateTime object and have conversion handled by Doctrine instead of using
a date string with a fixed format.

pass the name of the item source from the browser to the server - no need to get the data via complicated db queries

fixe #2827

refs #4883

 * http/response.php
 * config.php
 * response.php
 * files.php
 * idbconnection.php
 * app.php
 * user.php
 * template.php
 * share.php
 * db.php
 * icache.php & il10n.php

ensure getChildren() is called on an instance of Share_Backend_Collection

only remember password if the user changes the permissions, otherwise the user disabled the password protection