Stream attachment(s) to gfs. Sequence update via socket. Minor fixes.

[herpiko]

@dotovr Testing scope :

• Should be able to download huge attachment ( > 15MB).
• Should be able to cancel the attachment uploading and remove uploaded attachment. The cancel button will appears when hover the cursor over the attachment's label.
• User could use same account in different browser/computer. Do actions that breaks message sequence (save new message, delete message, move message to another box), and the message list in other client instance should be automatically updated.
• Fixes invalid cookies from pnsmailAdmin's

[emhaye]

Pesan dengan lampiran gagal dikirim

400 bad request
Request","message":"child \"attachments\" fails because [\"attachments\" at position 0 fails because [\"canceler\" is not allowed, \"hover\" is not allowed]]","validation":{"source":"payload","keys":["attachments.0.canceler","attachments.0.hover"]}}

[emhaye]

:+1: