erp5_web_renderjs_ui: html5_select: event option for notifyChange added. needs for determine event.type on parent gadget

i need it because use span for displaying icons in json form

/reviewed-on nexedi/erp5!697

/reviewed-on nexedi/erp5!713

of Free Subscription Request module and FreeSubscription_viewFreeSubscriptionRequest
view of Free Subscription

Extend`FTPConnector.listFiles` to sort files based on some server-side computed attributes of files.

This uses [`listdir_attr`](http://docs.paramiko.org/en/2.4/api/sftp.html#paramiko.sftp_client.SFTPClient.listdir_attr) method of paramiko. `sort_on` parameter is directly attributes of [`paramiko.sftp_attr.SFTPAttributes`]( http://docs.paramiko.org/en/2.4/api/sftp.html#paramiko.sftp_attr.SFTPAttributes).

At the same time, adds a minimal tests, that will only run if `testSFTPConnection_SFTP_URL` environment variable is set to an URI of a running sftp server supporting password authentication - which means that in our current tests infrastructure it will not run.

/cc @vpelletier @aurel @rafael 

/reviewed-on nexedi/erp5!680

/reviewed-on nexedi/erp5!711