Add support for attachments

[barryoneill]

Add support for retrieving/viewing attachments.

[barryoneill]

Ok - this is FINALLY in. Changes:

• /rest/messages/{messageId} endpoint now delivers an attachments block, for each attachment the following is present:
  • attachmentId - a unique identifier (in the scope of the containing message). This is actually the sequence number of the attachment's position in the MIME body.
  • filename - the filename as set by the mail client
  • contentType - associated content type
  • disposition - Either 'inline' or 'attachment' representing content embedded in the HTML body, or a standalone attachment respectively.
  • sha256sum - to let testers verify the contents of a message without having to fetch it.
  • size - the size in bytes of the attachment
• /rest/messages/{messageId} no longer delivers messageRAW attribute (performance degradation for attachment users). Use existing /rest/messages/{messageId}/raw* instead.
• /rest/messages now delivers an additional hasAttachments flag:
  • This only takes those attachments of 'attachment' disposition. Embedded 'inline' don't count.
  • This only works for new messages. Existing messages can be patched if desired with: update message set has_attachments=1 where message_body like '%Content-Disposition: attachment%';
• A new endpoint, /rest/messages/{messageID}/att/{attachmentId} will serve the content of the specified attachment with the appropriate Content-Type with a Content-Disposition setting the attachment's filename.
• Rudimentary RFC2231 has been added to support i18n in the MIME headers. This means that subjects and attachments (among other features) should now have multi-language support. (Message bodies previously had no problem).
• The UI has been updated:
  • The mail list now shows an icon to mark whether a mail has any non-embedded attachments
  • The mail details now lists any non-embedded attachments as download links.