Add support for flow.js "octet" method

[damienalexandre]

The PHP server only support the default multipart option, and not the octet one.

This should be added to the documentation right now,
and maybe added to the library as contributions go :)

• the Request must fake an upload array:

    $fileArray    = [
        'name'     => $requestParams['flowFilename'],
        'type'     => '',
        'tmp_name' => 'php://input',
        'error'    => UPLOAD_ERR_OK,
        'size'     => $requestParams['flowCurrentChunkSize'],
    ];

• the File::_move_uploaded_file method must not use move_uploaded_file but instead read 'php://input' and file_put_contents it