MDL-33409 Newly copied files should take on the userid of the current user, and dates...

MDL-33409 Newly copied files should take on the userid of the current user, and dates reset

- changed function repository::copy_to_area so it accepts more file attributes, pass changed attributes to it
- changed file_info::copy_to_storage and file_info_stored::copy_to_storage to accept more file attributes
- simplified file size check for moodle files in repository/repository_ajax.php
- removed unused code in repository/repository_ajax.php